Practical Manual - Malareo

Introduction to 

Geographic Information 

Systems 

Practical Manual 

QGIS for Malaria Page 1

Practical 1 Introduction to QGIS 

Outline 

Introduction 

Interface 

Menus 

Toolbars 

Map legend 

Map view 

Zoom/Pan/Bookmark 

Layers 

Adding 

Removing 

Visibility 

Viewing 

Saving 

Moving 

Types 

Points 

Lines 

Polygons 

Rasters 

INTRODUCTION 

This course assumes you have a basic working knowledge of computers and you know how to use 

Microsoft Windows and associated office software. It also requires a school level understanding of maps 

and mapping. In other words how to read a map and understand the concept of symbols representing 

points, lines and areas. There are basic mathematical operations such as basic Boolean logic and 

concepts required such as relative percentages. These are all required to effectively use GIS as a tool. 

GIS (Geographic Information System) is suited to epidemiology and mapping malaria as it allows you to 

map individual cases on a map where it was contracted. By mapping where the cases occur you can 

target the most affected areas appropriately and place resources where they are needed. By analyzing 


occurrences you can gain a better understanding of the spread of the sickness over time, such as when 

cases occur, are they linked to a particular event, such as a wet period 

QGIS is a desktop GIS, so named as it can be run on any desktop PC (Personal Computer). QGIS allows 

you to view, edit, analyze and output map or geographic (spatial) data. It uses amongst others, vector 

shape files (so called as the files have a .shp extension in the name) and raster layers to do this. 

Map layers (shape files) are loaded into the map legend one above the other and viewed in the map 

View / Display. 

There is a QGIS user manual which is also included in your root directory should you wish to delve 

deeper into the nitty grittys of QGIS. 

QGIS INTERFACE 

QGIS is opened by selecting it from the start menu in Windows, usually bottom left of your screen. Like 

most windows based programs it has its own window that can be minimized moved around or 

maximized on the screen. QGIS has a number of components that make up the program. 


These include: 

Menus such as: File, Edit, View, Layer and Settings amongst others and allow you to interact with the 

data and the program components. 

(These have drop down lists of all the tools and options available to you for use within QGIS). 

Toolbars contain shortcuts to selected icons representing many of the tools or options within the 

menus. 

(These allow one click access to the tool or option rather than having to search in the menus). 

The Status bar provides information on your map display and map layers, such as longitude and latitude 

(This helps you pinpoint locations and gives you information on the projection of the layers.) 

The Map Legend or table of contents (TOC) is where map layers are loaded and can be selected, and 

moved relative to one another in order 

(Layers are visible from top to bottom as if looking through a series of clear transparencies.) 

The Map view or Canvas is where the spatial data is viewed, essentially allowing you to view the map 

you are creating using the map layers in the map legend. 

(This is where you examine the map layers and change how they are represented to better 

express what you are attempting to show to the map reader.) 

Exercise 1. Opening a project 

Data can be added as individual layers to 

the map legend to make up a map. These 

layers can be manipulated (colors changed, 

line thicknesses altered) to create a map 

you wish to print or display. Once this is 

done the Map project can be saved. This 

saves all the settings used in the map. As a 

result you can open existing Map Projects. 

Open the Project called Africa. 

To do this left click on the Menu called File 

and select Open Project. 

Click on the drop down button to the right of the look in box and select navigate to the folder called 

malereo on your Local C drive (C:\malereo) folder. 


Once in the folder, using your mouse select (by left clicking on) the Africa.qgs project and click on open. 

This will open a thematic map (A map showing one 

attribute) of Africa Showing the number of cases of 

Malaria per 100 000 people in each country in 2008 

(WHO). 

Notice the Number of cases is assigned into classes 

to visually represent the severity of malaria cases. 

The QGIS window can be resized. To do this left click 

on the Maximize button in the top right of the QGIS 

Window. This expands the window to the maximum 

size of the screen and locks it in place. 

Menus 

There are 9 dropdown menus within QGIS, these allow you to interface with the software and the layers 

you have open. 

Exercise 2 Using menus 

Open the View Menu and select Zoom In. Using your mouse select a point to the south west of Libya, 

holding the mouse button down drag down to northern Mozambique. (A box will form showing the 

extent of your zoom and when you release it will zoom to the new extents. From the same menu select 

the identify item. Click on a number of the Countries, one at a time. Notice a identify results window 

pops up and relays information about each country. This is known as attribute information and is stored 

within the shapefile of the layer you are working with. In this case there is Country, Cases, Cases_km and 

Shape_Area. 

This is a major strength of GIS as you can query using both Spatial and attribute information. 

Within the View menu select Show bookmarks and select the Southern Africa bookmark. This “zooms” 

the Map view to the extents of Southern Africa. You can create your own book marks which make it easy 

to return to an area of interest while working with a map. 

Familiarize yourself with the menus and their contents, by opening each menu and scrolling down the 

menu. The file menu allows you to open and save projects and to print. 

The edit menu allows you to edit layers and features within layers 


View allows you to move around your view, zoom and identify features 

The layer menu allows you to add and remove layers and open attribute tables for the layers. 

Open the attribute table for Malaria_Cases_2008_WHO. 

The settings menu allows you to alter the settings within the software and project, such as changing 

your co-ordinate system. 

The Plugins refers to add on tools or programs that can be run within the program, for example 

interpolation. 

Raster allows you to undertake raster calculations on raster layers such as multiplying one layer by 

another. 

The vector menu has a number of sub-menus including tools for analysis and processing of vector data. 

Toolbars 

QGIS also contains a number of selected tools present within your Menus but made easily accessible by 

placing them on your main window. These tools are represented by icons and are arranged into 

separate toolbars allowing for a one click selection of a tool. The toolbars themselves can be turned on 

and off as they are needed or kept permanently on. 

As you move your cursor (pointer) with your mouse over each Icon, the name the tool represents 

becomes visible next to the icon, making it easy to find the tool you need. 

Find the icon that zooms to the full extent of your 

map (Zoom Full) 

Exercise 3 Using toolbars to add a vector layer 

Using your cursor find the tool to add a vector layer 

to your legend or project. The add vector layer 

window opens. 

Keep your source type as file and click on the 

Browse button in the Source section. 

Select the file Capitals_Africa.shp file and select open. This adds a new vector layer representing the 

capital cities for most Countries in Africa. 


Map Legend 

You now have 2 layers loaded into your map legend. Capitals _Africa and Malaria_Cases_2008_WHO 

Notice in the Map legend that each has a cross in a box to the left of the name of the layer. This 

indicates that the layer is displayed. 

You can make layers visible or non-visible by selecting the cross in 

the tick box. Click on the cross next to Capitals_Africa and examine 

the map view or canvas. Notice the layer is no longer visible. Play 

with the layer visibility for both layers. 

Layers can also be moved relative to one another. Using the mouse 

left click and hold down the left mouse button on the Malaria cases 

name in the legend. Keeping the left mouse button depressed drag the malaria layer upwards (A Small 

icon appears with 2 arrows). Drag it up and above the capitals layer. Note what occurs. Most of the 

capitals are no longer visible and are hidden under the countries. (You can still see a few present along 

the coastline.) 

This means that when displaying layers in QGIS you need to careful about the order you place your 

layers in. The general rule of thumb is points above lines above polygons. 

Move your layers back in order so that you can see them. 

Go to the file menu and select save project as: Name your project as your Name e.g. Joe and save it in 

the directory of your choice e.g. c:\temp\malereo\joe.qgs 

Saving a project stores the layers and their properties in a file which enables you to open it again and 

not have to reset all the properties. It does not however save any changes you have made to individual 

layers. This you will have to do separately when editing 

individual layers. And will be approached in a later 

practical. 

Map View 

The Map view is the area where you view the visible 

layers as listed in the Map legend. Here you can zoom in 

and out, View the layers and view labels of points, lines 

and areas. Any changes you make to the layer properties 

are reflected in the map view. 

Zooming 

There are a number of tools which allow you to interact with your view effectively. The ones you will use 

commonly are the Zoom tools. These are available both on the toolbar and in the View Menu. 


Use the Zoom in tool to zoom into South Africa. Place your cursor to the south west of south Africa and 

holding the left mouse button drag a rectangle over the extent of South Africa. 

Next you will Pan Use the Pan Map tool and Holding down the left mouse button drag the entire map 

southwards to show Botswana. 

Instead of having to use your Zoom out tool to get back to South Africa use your Zoom Last tool. 

Bookmarks 

You can also use book marks to Zoom to commonly viewed areas. Go to the view Menu and select Show 

Bookmarks. Select Madagascar. Notice the view shifts to Madagascar. Use the Zoom Full to Zoom back 

to the extent of the layers and create your own Bookmark for Eygpt and call it Egypt. To do this Zoom to 

Qygpt using your Zoom in and Pan tools, then select New bookmark from the view menu and type in 

Egypt. This stores a permanent bookmark that will allow you to instantly return to that view. 

Thus far you have had a brief introduction to the different components that make up the interface of 

QGIS and the layers and tools that are used. 

You will now look at layers and how you interact with them in more detail. 

LAYERS 

There are 2 main types of Layers that are used in GIS. These are Raster and Vector. 

Raster Data 

Raster layers consist of a grid of pixels, like a 

digital photo. The layer has a grid laid over it and 

each cell of the grid has a value, be that, a value 

representing red green and blue, as in an aerial 

photo, or a distinct value representing a theme 

such as soil type or malaria count. 

Exercise 4 Adding layers 

Add the raster layer Raster_cases to your map 

legend. Notice a single grey layer is displayed the 

approximate shape of Africa. Ensure you turn off 

the other layers in the map legend. 


Select the Identify features tool and select a 

number of pixels (one at a time around the 

continent.) An Identify results window pops 

up and shows the value at each point (chosen 

pixel). 

To Change the display to enable you to see 

differences right click on the raster_cases 

layer name in the map legend. A context 

window opens. Select Stretch using current 

extent. (This performs a contrast stretch 

using the minimum and maximum values of 

the layer). 

This illustrates that although the data is in raster format it is 

very similar to the vector layer showing the cases of malaria 

present in each country. It just has a very blocky pixilated 

appearance. Verify the data is similar. To do this turn the 

Malaria cases back on and highlight the layer. Then use the 

identify features tool. By changing which layer is highlighted 

in the map legend the identify features tool returns the value 

for that layer. 

Can you answer this Question 

How many cases did Mozambique have per 100 000 people in 

2008________________________________________ 

Add the Tiff image Africa_150m_earthsat.tiff to your view and move it to the 

bottom of the map legend. You will use this layer in the visibility portion of the 

practical 

Removing layers 

There are a number of ways of removing layers. The first is to use the Layer 

Menu and select remove layer(s). This will remove the highlighted layer(s) in 

the Map legend. To select more than one layer at a time in the map legend 

hold down shift and left click on multiple layers. 

The second way of removing layers, which you will undertake is to right click 

on the layer raster_cases in the map legend. Ensure that only the raster_cases 


is highlighted, then right click on the layer name. This brings up a context menu, select remove from the 

menu. This removes the layer from the project. If you were to save the project it would not include the 

raster_cases layer. This is therefore different from turning a layer in the legend off. All layers can be 

turned on or off at once using “Hide all layers”. They can also be turned back on by selecting “Show all 

layers”. 

Visibility 

As mentioned above layers can be made 

visible or turned off using the tick box 

next to the name of the layer in the map 

legend. (You have done this already in a 

previous exercise) There are however 

other ways of changing the visibility of a 

layer. The way that layers are displayed is 

dependent on the properties of the 

layer. 

Exercise 5 

To view the Malaria cases layer 

properties right click on the layer and 

select properties from the context menu. 

This opens up a Layer properties window. 

There are a number of Tabs at the top of the page. The far left tab is the Style 

page. Select the style page tab if not already active by left clicking on the tab. 

Directly under the Style tab is a drop down which is currently set to Graduated. 

Left click on the small inverted triangle next to Graduated. A drop down 

appears with a series of options including Single symbol, Categorized and 

Graduated appear. Select Single Symbol. 

Now click Apply at the bottom right of the layer properties window and finally click Ok. Notice that the 

Malaria cases layer is now a single colour with solid black lines representing the country borders in your 

Map View. By modifying the style of a layer you can change how a layer is represented on the map view. 

Notice also that when you changed the style to single symbol the options within the style tab also 

changed. 

Notice next to the Unit Color is the word 

Transparency 0%. To the right of this is a 

slider. Drag the slider to 30% by left clicking 

and holding down the left mouse button and 

dragging the slider to the right. Notice the 

colour becomes less and less visible. Once at 


30% release it and click on Apply and Ok. Notice you can now see the raster layer which is a satellite 

image of Africa through the Malaria Layer as it is now partially transparent. 

Saving Layers 

When working with GIS data it is advisable never to work on your original data. The reasons are, if the 

software crashes or the user makes a mistake by deleting features or data the original unaltered data is 

still available from to start with again. It is also worthwhile saving in progress files if modifying or editing 

data. It is advisable to save copies atleast each day if not every few hours. In the following exercise you 

will make a selection of data and save that as a new layer. 

Exercise 6 saving a selection 

Open the Project called Selection. In order to save a selection you first need to 

make a selection. The easiest way to do this is to select by polygon. Find the 

tool on the toolbar or in the view menu that says “select features by rectangle” 

Hold down the left mouse button and drag a rectangle over the Southern 

African countries. You will notice they become highlighted in yellow. 

Right click on the Malaria Africa_2008 layer and select the “Save Selection as”. 

Choose your directory and call the output Southern Africa. 

You have now created a new layer of just the Southern African Countries. 

Add this layer to the Map legend to view the layer. 

Moving Layers 

Linked to visibility is how layers are viewed relative to one another. By selecting a layer in the Map 

legend, holding down the left mouse button and dragging, layers can be moved relative to one another. 

Take the Southern African layer and drag it to underneath the Malaria layer. Notice it disappears even 

though it is still in the map legend. It is worth checking the order of layers in the map legend if data is no 

longer visible. 

GIS data: Layer Types: Vector Data 

There are 3 Main Types of Vector data. These are point line and polygon. 

Line using Point nodes with Co-ordinates (X,Y) (Source: University of Washington ERM250) 


Point layers consist of an X and Y co-ordinate (and occasionally a Z (Height)). These can be in Geographic 

projection (Longitude and latitude), using the number of degrees in a compass direction from the 

Equator and Greenwich Meridian to give a point it’s relative position. 

Longitude: 

Latitude: 

Or they can be in a projected format, using metres measured along the earth’s surface again from a 

reference point or line. 

Examples of point data include households, Hospitals, Clinics, Schools, points of infection etc 

The usual format used is degrees decimal where the X is Longitude (lines running along the Globe) and 

Latitude Y with line running Around the globe e.g. 29.765437(E), -31.99864(S) 

Move your cursor around the screen and look at the status bar at the bottom of the screen. Notice the 

co-ordinates change as you move the cursor around the screen. 

Line layers are point layers that have the points joined by a line. These lines have a distance and 

direction associated with them, but the principal is the same, using x and y co-ordinates to specify nodes 

between lines. Examples include Roads, railways, Power lines, Rivers etc. 

Polygon layers are lines that have been joined to form a continuous line surrounding an area. The 

polygon has a perimeter and an area. Areas can be measured un Decimal degrees but it is prefereable to 

measure them in square metres or hectares. To do this it is often necessary to use a projected layer. 

Examples include Municipalities, Wards, Census districts, Dams, Cadastral (Property) boundaries etc. 

There are various levels of vector data. For example Country boundaries can be further broken down 

into Provinces, Then Magisterial Districts, and then Wards. In the following exercise you will look at 

various layers in map view to get an idea of the different types and scales of data. 

Exercise 7 Vector Data. 

Open the project Vector_Data. 

This project contains 6 layers. 3 polygon, 2 line and 1 point layer. 


It is important to note that although layers may represent the same general area, they may be collected 

at different scales and by different people and as a result may not match each other. 

When working with data you need to have a good understanding of what each layer represents. The first 

thing to do when examining data is to gain an understanding of what is being represented. What do the 

points lines and polygons represent This can be done by examining the layer name and then by 

examining the attribute table of the layer to see what the layer contains. Some data contains meta-data 

which is information about the layer and what it contains, its accuracy, date, file type etc. 

Open the attribute table for the Health facilities layer. (Right click on the layer and select open Attribute 

table.) Notice the 2 columns Longitude and Latitude. Notice the format of the information. Look at the 

various column headings. You can gain a better understanding of the data by looking at the attribute 

information. 

Name 5 of the types of facilities in this layer 

___________________________________________________________________________________ 

Close the attribute table. Now right click on the Layer Power_lines and select zoom to layer extent. The 

map view zooms to show the layer at the maximum possible extent while still fitting the whole layer into 

the view. 


Open the attribute table. Notice there are no Longitude latitude columns but there is a shape length 

column. Notice the figures, (Very small numbers) these distances are in degrees, which are not constant 

dependant on where you are on the globe. 

To get an idea of distance you will now measure a length of 

Conductor. Go to the bookmark Measure. Select the measure line tool 

from the toolbar. Starting at the top left of the line using the left 

mouse button click along the line following the line to its end. Notice 

in the pop up window the distance is shown in metres and the 

distances increase with each added click. 

What is the approximate total length of the line 

Next you will look at the relative accuracy of layers. Open the bookmak Scale. This is an area on the 

Orange river on the border between South Africa and South West Africa 

Notice that while at full zoom differences between the layers 

are not visible, but when zoomed in you can see the lines 

although similar do not coincide. When undertaking analysis 

or editing data, this can cause problems. Be aware of the data 

you are using. 

Notice how the river has 2 lines (one on either side of the 

border representing the width of the river.) Also notice that 

the SA Provinces do not match the Boundaries for South 

Africa. (This is because they are from different sources and 

digitized (created) at different levels or scales. You can use 

the Zoom Last tool to zoom to the last view extent or zoom 

full to zoom to the full extents of all layers. 

Be aware of these issues when acquiring or using different data sets. 

Raster Data. 

Open the project called raster. This project contains a Digital elevation model, where each pixel 

represents the average altitude across that area of land in the country. The pixel size is 800m x 800m. 

Notice there are vector layers present in the Map legend. Turn these on. Do the rivers match the 

Elevation 

Zoom into a river. Notice the size of the pixels get larger as you zoom in while the vector lines stay the 

same thickness. This is one of the advantages of vector GIS over raster GIS. Symbols used to represent 

lines and points will stay the same point size irrelevant of scale or zoom. However pixels have a set size 

and will increase or decrease in relative size as you zoom in or out. Use the Zoom bookmarks to show 

this or zoom in interactively. 


Open your Identify features and examine the values of pixels for both Raster layers. Notice that although 

there are 2 Raster layers displaying elevation, only the Africa_Elev contains the actual height values. The 

colour image contains red green and blue values and cannot be used to determine altitude, but can be 

used to drape over an elevation layer to increase visibility or contrast. Use your transparency to make 

the Africa layer 70% transparent. Zoom to the full extent of your map and examine your map. 

Again it is important to know your data and determine what each layer represents. 

Challenges 

The following exercises are optional but allow you to interact more intensly with the software. 

Undertake the following: 

Create a map of Africa integrating the Africa Elevation data with the malaria_2008 cases data and Rivers. 

Save the output as a JPG image 

Using Any Project Zoom into South Africa at a scale of 10 000 000. (Use your scale window) and add the 

Rivers_SA layer. 

How Many Countries are there in the Malaria_Cases_2008 layer 

What is the Mean number of Cases for Angola, Zambia and Mozambique Combined 

Using the basic statistics tool, determine the Mean number of cases of Malaria across Africa 


Practical 3 Data capture, Preparation and digitizing 

Outline 

Introduction 

Acquiring Spatial Data 

Data Formats 

Opening Spatial Data 

Opening Attribute (Tabular) Data 

Creating Spatial Data 

From Attribute Data 

Preparation 

Conventions (Formats) 

Creating a Layer from CSV 

Digitizing Spatial Data 

Creating a New Vector Layer 

Points 

Scale and accuracy 

Snapping 

Lines 

Polygons 

From GPS 

Introduction 

A map is only as good as the data it contains. There is an old GIS acronym which is still applicable today: 

GIGO: Garbage In Garbage Out. If your data is poor, no matter how good your analysis or map making 

skills are and output will be weak. It is important to get the best possible data available and to ensure 

that your data capture is done in a standardized, systematic and reproducible manner. This practical is 

all about getting data into GIS. 

There are numerous data GIS packages on the market and as a result, different data formats that are 

used in GIS and CAD (Computer aided Design). This makes the task of standardizing important. QGIS is 

freeware and has been designed to function with numerous data types, these include: 


Acquiring Spatial Data 

There are numerous types of data available and the sources of these data are varied. The quickest and 

easiest source of data is the internet and a fair number of the coverages (layers) you are using come 

from the internet. However data often has restrictions associated with it, be that in terms of distribution 

or utilization. Often free data is made available for education and research but not for profit. Also as the 

data is free there is no guarantee of accuracy or content. This needs to be taken into account. A highly 

accurate source of data is usually government departments especially the Surveyor General of a 

country. Data providers can also be employed to acquire data, be that from aerial photography or 

individual GPS surveys or projects. How you source data is dependant on the needs of the project and 

the budgets available. 

GIS Data can be acquired from various sources or using various means. These include government 

departments, Data vendors, the internet, from a GPS, on screen digitizing, importing images and georeferencing 

them and importing CAD diagrams and converting formats. 

A number of sources of data include: 

Diva GIS http://www.diva-gis.org/gdata 

GeoSpatial Portal http://www.opengeospatial.org/ 

Free Maplibray http://www.maplibrary.org/ 

The Protected Planet (Conservation Areas) http://protectedplanet.net/ 

The USGS http://glovis.usgs.gov/ 

Therea re literally dozens of sites available for downloading data, each with their own requirements. 

Go to the DIVA GIS site on your browser and Download the Administrative boundaries for South Africa 

(if you do not have an internet connection these are available in your data folder. 

Most data is in a zipped format (8.zip or *.rar) and will need to be extracted into a usable data type or 

format. In most cases this will ultimately be as shape files. 

Data Formats 

There are numerous data formats that are used by different GIS systems. These include but are not 

limited to: 

ESRI Shape files (*.shp) 

ESRI Personal Geodatabase (*.mdb) 

ArcInfo Ascii (*.e00) 

MapInfo (*.tab) 

Microstation (*.dgn) 

Comma Delineated text (*.csv) 


Autocad (*.dxf) 

ERDAS (*.ecw) 

Geotiff (*.tif) 

Jpegs (*.jpg/jp2) 

ArcInfo ASCII (*.asc) 

These data types can be found by 

looking at the data type when you 

browse for layers in the add Vector or 

raster layer tools. When working with 

GIS it is possible to load carious 

different data types into one map. 

However it is advisable to standardize 

on one data type (convert data to one 

type) and work with one projection. 

The most common form of data type 

currently utilized in most arenas is the 

ESRI shapefile. It is seen as the 

industry standard. It is highly 

interchangeable between different 

systems and has been around for a 

long time (+-20 years). As a result it 

can be used in most GIS software 

packages. 

There is a move towards Geodatabases but often shapefiles as they are tried and tested, work well. 

Opening Spatial Data 

Previously you have opened a project and loaded layers. In this exercise you will start with a blank 

project and load different types of data to create a project. 

Open QGIS, you will be presented with a blank Map view with no data in the Map Legend. You will now 

load a series of Map layers. 

Load the Shapefile called Provinces_SA. This is a layer of the Provinces of South Africa as of 2006. To do 

this Select Add vector layer and Select Browse. From the Files of Type drop down Choose the type as 

ESRI Shapefile and select Provinces_SA_2006.shp and click on open 


This adds the shapefile to the legend and view. 

Next you will add a CAD layer consisting of the Provinces of Zimbabwe. 

Add a vector layer and choose DXF as the input type (This is an Autocad Format) Select 

Provinces_Zim.dxf from the Directory and select open. Notice it add a layer called entities map legend 

and places a series of polygons into the map view. Zoom to full extents to view the layers. Right click on 

the layer and open the attribute table. Notice there are no Province names associated with the polygons 

(this is a problem with importing CAD to GIS, as each separate layer including text entities are separate 

layers and as a result the labels are in this case lost.) 

Next you will import a geodatabase file for Mozambique. Start by selecting Add a vector layer and select 

the file type ESRI personal Geodatabase [OGR] (*.mdb *.MDB) and select Mozambique.mdb from the 

directory. Select open and Open again. This brings up an interface asking you to select a layer, Choose 

Provinces_Moz from the list and click on OK. 

This loads the Provinces for Mozambique into the Legend and onto your view. If you open the attribute 

table, notice the data assosciated with each polygon is still present, unlike with CAD. 

Next you will add a comma delimited Text file. There are 2 ways to do this. First as an attribute table by 

adding a vector layer and the second is as a spatial layer by Selecting Add delimited text layer from the 

layer Menu. This allows you to create a spatial layer from a text file You will undertake both. 

Select Add vector Layer and scroll down to the file type CSV and choose the Moz_Places.CSV 

Click on Open this add the attribute table to the legend, but does not add the Spatial entities. 

Opening Attribute Data 

To view the attribute table, Right click on the layer name MOZ_Places and 

scroll down the context menu to Open attribute table. 

In the Attribute table you will notice the fields and the data populating 

them, but there are no spatial entities in this instance as you have merely 

added a table to the map legend. Being able to import attribute data only 

is useful as it can then at a later stage be linked to a spatial layer using the 


attribute information for example the column called “name”. We will look at linking later in the course. 

Go to your file menu and choose save project. Choose a file name to save it as e.g. Southern_Africa.qgs 

and save it in your practical 3 Folder. 

You can now open the project directly instead of having to add each layer individually. However this 

does not preclude you from adding extra data to the project. The project can continue to grow or shring 

as you add or remove layers to get to the product you want. 

Creating Spatial Data 

In the exercise above you opened a number of different GIS layers. Each one was in a different format. 

You added: 

a shape file (provinces_SA.shp) 

a CAD layer (provinces_Zim.dxf), 

a geodatabase file (Mozambique.mdb) 

and finally a text file Moz_places.csv. 

Each one of these files is a different type of data with different properties. When working with GIS it is 

not necessary to work with just one type of data, however it is highly advisable. It is a good idea to 

standardize on one type of data as it removes possible errors or shortcomings of one of the data types 

you are using. For example CAD not having a complete attribute table when imported. (The labels 

(Attributes) are stored as a separate text layer) 

Data Preparation 

In order to ensure the data you are opening or creating is of suitable quality and of the standard require 

it is often necessary to ensure the data is properly prepared. 

The last data you added was a text file and was added as an attribute table. When adding a delimited 

text layer you are not limited to just adding it as an attribute layer. If the layer contains spatial 

information in the form of Longitude and latitude it is possible to add it as a spatial layer. You will 

undertake this now. First though you need to ensure the data is in 

the correct format and properly arranged. 


You will be creating a layer using a text file. In order to do this you must validate your data. 

Open the text file called Moz_places using excel. 

table. 

Expand all the columns to 

enable you to see the cell 

contents. In order to import 

spatial data from a table 

you require 2 columns, each 

one representing the X and 

Y location of each point you 

wish to show. You can 

name these X and Y or Long 

and Lat or any name as long 

as you can identify it in the 

Conventions 

Ensure that the columns f the X and Y co-ordinates are of type Number and check they have atleast 5 

but preferably 8 decimal places. Also check if the Y co-ordinate is negative (as you are south of the 

equator.) If you make it positive it will place your points upside down in the northern hemisphere. 

Other columns can be of type general as they will be text generally, however any numbers must be of 

type numeric. (For example population data etc.) Also at this stage check for spelling errors. Also make 

sure you have not transposed the X and Y columns as this is a common occurrence. 

Save the Excel Spread sheet as a csv file or close the table if all the data is in the correct format. 

Creating a Layer from CSV 

Create a new project. Using either the New project tool 

on the toolbar or the menu item under file menu or use 

the shortcut key cntrl-N 

This creates a blank new project. 

Select add delimited text layer from the layer menu 

This opens up The “Create layer from a delimited text 

file” window. 

Browse and find the csv file called moz_places 


Within the window select selected delimeters and choose comma as the type 

Choose X Y fields and select LONG for the X field and LAT for the Y field 

Select OK 

You are then asked to choose a projection. Use the default which should be WGS84 and select OK 

This creates a spatial layer of all the places within Mozambique. If they are not immediately visible 

zoom to layer extent 

To save this layer right click on the layer and select 

Save as 

Choose your format as Shapefile, Browse to your 

destination directory (Prac3) 

Leave the CRS as default 

and save it as Places_Moz.shp by selecting OK 

You have effectively added spatial data from a text 

file by creating a spatial layer in the form of a shape 

file. 

Often you are required to create data from an aerial photo or an image, in essence to simplify the 

image. For example an aerial photo or Google may contain trees, houses, roads, dams and rivers. You 

only need to see the houses and the rivers. You would therefore want to create layers that can be easily 

seen and kept separate for each feature you are interested in. 

The process of creating or modifying a vector GIS layer is called digitizing (Making it digital) 

Open the Project called Digitising. You will see and aerial photo called Howard_College. This is a 

panchromatic (Plack and White) tif image that is geo-referenced. It is an aerial photo of the Howard 

college campus where you are currently located. Notice as you move your cursor around the map it 

shows the location as being geographic 30.98…. and -29.86…. (This can be used as an indicator of the 

projection system used). 

Creating a New Vector Layer 

In order to start digitizing you will need to create a new layer To create a layer from the layer menu 

select New Shapefile Layer 


This opens a co-ordinate reference system selector. As the layer you are viewing (Howard _College) has 

a Geographic Co-ordinate system (Most Geographic co-ordinate systems use wgs84 as their datumn) 

you can select the WGS84 Co-ordinate reference system or projection. 

In the New Vector layer window you have the option 

to add attribute fields. 

You will add one more field called “Building” 

To do this, within the New attribute section type in 

“Building” next to Name 

Below this is a drop down option to choose the type of 

data. We will use Text Data as we are going to name 

some of the buildings. We don’t however need 80 

characters so change this to “50” 

Now click on the Add to attribute list and the field is 

added to the list of attribute fields (columns in the 

attribute table) 

Click on OK 

Select WGS84 and click OK. 

This presents you with the New vector layer window. 

It is here you select the type of vector layer you will 

create. 

We will create all three types of layers point, Line and 

Polygon, starting with point 

So select the type as point 

Leave the CRS ID as WGS84 as you chose in the previous 

step. 

This opens the Save as Window. It is here you get to 

name the layer you are creating. Within the File Name type “Buildings”, Make sure the directory you are 

saving it in is the Prac3 folder and Select Save. 


You will notice a new layer called Buildings with 4 small dots to the 

left of the layer name has been added to the legend. 

You are now ready to start digitizing. 

To start digitizing you need to make sure the layer you want to edit or digitize is selected (Highlighted 

within the legend) Then select the Toggle Editing tool Either in the Layer 

Menu or from the Toolbar 

You will notice that the Buildings Layer now has a Pen next to the layer name and not the 4 dots. 

This indicates that you are in edit mode. 

Use your zoom in tool to zoom into the building in the North east 

corner of the image (T shaped building with a dark Roof). 

Select your Add Point tool on the toolbar and select a point using 

your left mouse button at the intersection of the two roofs or a 

point as close to the centre of the building as possible. A Attributes 

window opens. Type In “1” as the id and “Administration” in the 

Building Field. 

Once complete click on OK. 

You will now see a coloured dot where you selected your point for the 

building. 

Add 4 more points one for each building you choose and call them 

Memorial Tower, Old Main, Social Science and Management. 

To stop editing, toggle editing off. You will be asked if you wish to save 

the changes. Select “Save” 

If you have made erros you have the option to discard. 

Cancel will return you to editing mode. 

To view your edits turn the Howard college image off and 

zoom to the Layer extents of the Buildings layer. 

Challenge: 

See if you can label the points on your own. (Hint: 

use the layer properties.) 

You should see a layout similar to the one shown. 


Next you will create a line layer (line layers are also refered to as polyline layers, poly meaning many) for 

the roads. 

To do this, add the layer HC_roads to the legend. (This is a blank line layer with attribute fields called 

Road and Length) 

Scale and accuracy 

An important consideration when digitizing , is the scale (Zoom) at which you will digitize. This is highly 

dependant on the needs tof the work you are doing and the required precision. If you zoom out too 

much you will not be able to see details in an image. But is you zoom in too much sometimes depending 

on the quality of an image you will also not be able to see a lot. 

This is shown below: 

Too zoomed out 

Too Zoomed in 

On the image on the left it is too zoomed out to allow for accurate digitizing (You need to be able to 

accurately or precisely follow roads. On the image on the right you are so far zoomed in that the image 

appears distorted. Therefore a balance needs to be found. 

It also helps to maximize the size of your QGIS window. This gives you a larger view of the layers. 

Maximize your GIS window. In order to set your zoom type 1:500 into the zoom window in the status 

bar at the bottom of the QGIS window. Of course if you are digitizing at a provincial level you would 

zoom out a lot more 1:10 000 for example 

In this case 1:500 is a reasonable scale to digitize at as it allows objects to be seen clearly. 


When working with lines and polygons it is often necessary to be able to join them. For example roads 

join at intersections. When digitizing roads, should share common points at their intersections. To 

ensure this happens you need to snap points to one another. To enable snapping Go to the settings 

menu and select Snapping options. This opens the snapping window. 

You will be editing the HC roads layer so you want to select HC_Roads and make it snappable. To do this 

check the box to the left of the name of the layer you wish to make snappable. 

The mode you want to use is to allow the roads to meet at vertexes (to share a common point) 

So choose vertex for the mode and then change your snap tolerance to 10 and change the units to 

pixels. What this does is if your cursor is within 10 pixels of a vertex the line you are digitizing will snap 

to this vertex. This also means you cannot have vertexes within 10 pixels of one another. 

Click apply and ok 

Start editing the layer. 

When digitizing a network for example roads or rivers you need to look for possible points of 

intersection with other lines. If there is a side road off the main road you need to place a vertex at the 

intersection point. This allows you to join another road at the intersection. 

Start digitizing by scrolling your image to the far right. You can see 2 rows of parked cars on either side 

of the road (visualize the road you came in on this morning (further east is the boom gate). Select the 

capture line tool from the digitizing toolbar. Move your cursor to the edge of the image and start left 

clicking along the centre of the road. Moving in a westerly direction there is na intersection to the north, 

make sure to place a vertex in the middle of the intersection keep moving left. You meet a number of 

intersections along the road. You then meet a turning circle go around the turning circle being aware of 

the road meeting it to the west. Eventually you will get back to the road where you wil move your cursor 

close to the line and select an exisiting vertex on the road. Once this is done right click. This brings up 

the Attributes window. Select id as 1 and the road as entrance. Don’t worry about the length at the 

moment. 

Click on OK. This section of the road is now digitised. 


Continue digitising the other roads around the campus, 

making sure you snap vertices to roads. 

Eventually you will run out of window to digitise in. 

When this occurs select the pan tool and drag the 

window eastwards so you can see more of the road 

network. Then reselect the capture line tool and you 

can cintunue digitising from where you left off. 

If you inadvertently don’t get a line to snap to a vertex 

you can use the Node tool. Select the node tool move 

your cursor over a a section of road. Left click to select 

the segment and then move your cursor dirctly over a 

node (vertex) on the line and left click again. You will 

see the vertex changes colour to blue. This indicates the 

vertex is selected. You can now move the vertex by 

dragging it by holding your left mouse button down with 

your cursor on the vertex and dragging it to another 

vertox or to the point where you want it moved. 


Once you are happy with your line layer you can toggle editing off and save the layer. Be creative with 

your road names. 

Polygons 

Digitising polygons is essentially the same as digitising lines. The difference is that a polygons must have 

congruent side and must not overlap. To ensure common boundaries enable the topological snapping 

option for the layer you are digitising. 

Within GIS dependant on the scale you are working at it could be preferable to digitise a point versus a 

polygon. For example: Tress can be represented as polygons or as points. If you want to show the 

location of a tree or it is preferable to use a point however if you are working with tree canopy’s and 

want to deternine area of all tree canopies then polygons would be preferable. The decision as to how 

to digitise is dependant on your need. 

Challenge: 

Create an polygon layer called HC_Buildings and digitise the outer extents of each building that you 

represented as a point in your buildings layer. Remember to name them. 

GPS data 

GPS units such as the Garmin or 

Magallan handheld units allow 

you to store waypoints and 

tracks as you move around. A 

prime example would be 

mapping the location of a 

homestead where a case of 

malaria was found. 

There are various formats that are 

used to transfer GPS data from the 

GPS units to GIS one of these is the GPX format GPS Standard Exchange Format. This can be used by most GPS 

units and GIS systems to transfer data. There are numerous freeware programs to download files should you want 

to create basic text files instead of importing them directly into a GIS. The include G7toWin and DNRGarmin. 

In this exercise you will import a GPX file into a 

new project and add a Spot image as a back drop. 

Create a blank project. Select the GPS Tools. This 

opens the GPS Tools window. Select the Load GPX 

file tab (top left tab)Browse to find the 

GPS_pnts.gpx file from your prac3 directory and 

select it. Make sure waypoint types are checked 

and click ok. 


If you are interested in seeing the format you can view the GPX file in notepad or a text viewer. As you can see this 

file was created by DNR Garmin as this file was downloaded using DNR Garmin software. The text format is 

however vastly different to a standard csv file. When working with GPS data it is often worth saving the GPS data 

into both a gpx and a csv file to ensure no loss of data. 

Next you will load the backdrop image. Add a raster layer called Umfolozi. This is a spot image clipped to the 

extent of the main study area. In this case the points are locations soil samples within Hlhulwe-Umfolozi Game 

reserve. 

It is always safer to save a GPS event theme (waypoint layer as a new shapefile and you can do so by 

right clicking on the layer and selecting Save as. 

This practical has introduced you to the concepts of acquiring data, opening data, importing data nad 

creating your own data through digitizing. The QGIS manual contains further details on Data capture and 

digitizing. The manual is included as a PDF in your course notes. 


Practical 4 Coordinate Reference Systems (CRS) 

Outline 

Project Coordinate Reference System 

Changing the default setting 

Enabling "On the Fly CRS" 

Layer Coordinate Reference System 

Determining the CRS of the layer 

Changing the CRS of the layer 

INTRODUCTION 

QGIS refers to its projection and datum environment as the CRS (Coordinate Reference System). QGIS 

supports 2700 known Coordinate Reference Systems, defined by the European Petroleum Group (ESPG) 

and the Institut Geographique National of France (IGNF). These are stored by QGIS in the SQlite 

database. QGIS also supports "on the fly" (OTF) projections. This allows one to define the CRS of each 

new layer "on the fly" without having to change the properties of that layer. 

When deciding on what projection to specify for the project you are going to be working on, it is 

important to take into account the types of analyses you will be doing. For example, if you are going to 

be working primarily with locations then a Geographic Coordinate System is sufficient. However if you 

are going to be doing any type of length, area or other spatial calculations, then it is important to use a 

Projected Coordinate System, and bear in mind the units that the system uses. 

(WGS 84 is a Geographic Coordinate System, UTM is a Projected Coordinate System and uses meters (m) 

as its units). 


PROJECT COORDINATE REFERENCE SYSTEM 

QGIS specifies, by default, the Global and Project CRS as WGS 84. This default can be changed. It is also 

important to be able to set the default action that is carried out when adding a layer that has no 

specified CRS. These functions are all carried out in the CRS Tab of the Project Options Window . This is 

accessed using the Settings Menu and then selecting Options. 

Changing the default setting 

 

Access the Project Options Window by clicking on the Settings Menu in the Menu Bar and 

selecting Options. 

 

This brings up the Options Window. Select the CRS Tab. It is here that the default settings for 

QGIS' CRS can be configured, as well as the default way in which QGIS responds to new layers 

that do not have a specified CRS. It is also here that "On the Fly" projections can be set as 

default. 

Set the Default CRS and OTF Projection Options 

Set the Default way that QGIS responds to layers with no specified CRS 

In the first section, the default Global and Project CRS is specified. This is done by clicking on the 

Select Button and choosing the default CRS of choice from the list. 

In the second section, the default way that QGIS responds to layers without a specified CRS is 

selected. In this there are 3 options: 


o 

o 

o 

Prompt for CRS: This option will open a window and request that the CRS of Layer be 

specified. 

Use Project CRS: This option will apply the default CRS of the Project to the Layer. 

Use default CRS displayed below: This allows the user to choose a default CRS that is 

different to the Project or Global default CRS to be applied to new Layers. 

The CRS dialog box contains 5 areas of importance: 

 

 

 

 

 

Enable OTF transformations 

List of available CRS 

Proj 4 Text, information from QGIS about the 

projections 

A search option to assist in locating a specific 

CRS. This search can be based on the EPSG 

code, CRS identifier, or CRS name 

Recently used CRS is a list of the most recently 

used CRS in QGIS. This is useful if there is a 

particular CRS that is used often. 

Enabling "On the Fly" projections 

QGIS supports "On the Fly" (OTF) Projections. This means that QGIS is able to reproject layers into 

different CRS without the need to permanently change the CRS. However, OTF is not activated by 

default and needs to be turned on. There are three ways in which to activate OTF. 

 

 

 

From within the CRS Tab of the Project Properties Dialog Box. 

Click on the CRS Status icon in the bottom right of the task bar. 

Enabling OTF by default in the Properties Dialog Box. 


Task 1: Changing the Default CRS in QGIS and setting OTF projections as Default 

 

 

Open a new QGIS project. 

Access the Project Properties Window. 

By default the CRS should be WGS 84. 

 

 

 

 

To change the default CRS, search the list of CRS 

and find Cape/UTM Zone36S. (Look in the Universal 

Transverse Mercator submenu). 

Once this has been found, click on it to select it. 

To enable OTF projections, check the box at the Top 

top of the window marked Enable "on the fly" CRS 

transformation. 

Finally Click on Apply, then OK. 

The Default settings for QGIS have now been changed. In 

order to continue, go back and change the default CRS back 

to WGS84. In the Project Options Window, make sure that 

the Default manner in which QGIS deals with layers without 

a defined CRS is set to Prompt for CRS. 

Task 2: Working with Layer CRS 

 

 

 

 

 

Open a new QGIS Project. 

Add the layer called Fire_Stations from the Projections Data Folder. 

Next add the layer called eThekwini from the Projections Data folder. 

You will notice that a window has now opened and we are required 

to specify the CRS of the eThekwini layer. This is because the 

eThekwini layer does not have an associated CRS/projection 

specified (there is no .prj or .qpj file). 

Select WGS84 as the projection and click ok. 


You will notice that the layer does NOT appear in the map, however it is available in the TOC. 

This is because the CRS of the 2 layers are different. 

Open the metadata tab of each layer and look at the Coordinate Reference System. Make a note 

of what CRS each layer is using. 

It is important to get these layers into the same CRS if they are to overlay properly in the map. 

Use the Zoom Full button to see where these layers are sitting. 

Right click and select Set Layer CRS from the context menu. 

Specify the CRS as WGS84. 

Click OK. 

You will see that the Fire_Stations layer has moved. 

You can now see the difference in 

position of the layers. 

Remembering that the default CRS of 

the project is WGS84 and along with the fact 

that the eThekwini layer now has a CRS of 

WGS84, we need to change the CRS of 

Fire_Stations to match that of eThekwini. 

 

Select the Fire_Stations layer. 

If you use the Zoom Full button again you will notice that the layers are now overlaying nicely. 

However of you look at the scale bar, you will notice that it reads 40000 degrees in length. This is 

obviously not correct. 

To get the correct scale it is necessary to move the project and layers into the Cape/UTM Zone 36S 

projection. 

 

First Set the CRS of each layer to Cape/UTM Zone 36S 

Finally chance the CRS of the project to Cape/UTM Zone 36S. 

 

 

Zoom to the extent of one of the layers. 

You will notice that the scale bar now reads 40km. This is an accurate scale. 


Practical 5 Tabular Data Queries 

Outline 

Attribute Tables 

Viewing Attribute Information 

Working with Attribute Tables 

Selecting Records 

Selecting Multiple Records 

Switching and Clearing Your Selection 

Basic Statistics 

Querying Data in Attribute Tables 

Search 

Advanced Search 

INTRODUCTION 

GIS data has two components: 

1. Spatial (geographic) data which can be viewed as points, lines or polygons on a map. 

Points Lines Polygons 


2. Attribute data which describes the spatial data and can be viewed as a table. 

The following terminology is generally used when referring to attribute tables: 

An attribute table is a tabular file containing rows and columns. Each row (or record) in the 

table is associated with one geographic feature while each column represents an attribute of 

the geographic features. 

A field is a column in a table. Each field contains the values of a single attribute. 

A record is a row in a table. Each record contains the attribute data for a particular geographic 

(spatial) feature. 

Task 1: Viewing attribute information 

 

Open QGIS and load the Africa layer from the Tabular Queries folder. In the Map Legend, rightclick 

on the name of the Africa layer and select Open Attribute Table from the menu that 

appears. Browse through the table of attributes. 

Task 2: Working with attribute tables 

 

 

Selecting records: Move the table so that both the Map and Table are visible. Use the 

record selector buttons on the left of the table to select individual records. Look at the map to 

see how the records you select are also highlighted on the map. 

Selecting multiple records: Select multiple records from the table by holding down the 

key and clicking the record selector buttons. Look at the map to see how the selected features 

are highlighted. Click the Selected button at the bottom of the table to show only the selected 


ecords. 

 

 

Switching and clearing your selection: Make sure that all the records are shown by clicking on 

the first record, holding the SHIFT button, scrolling to the last record and clicking on it. Switch 

your selection by clicking the Invert Selection button. 

Basic statistics: Click on the Vector menu, then select Analysis Tools and then Basic Statistics. 

Ensure your Input Vector Layer is Africa and the Target Field is POP_ CNTRY, then click OK. 

What is the highest population of a country within Africa 

What is the total number of countries within Africa 

What is the Mean Population 

Task 3: Querying data in attribute tables 

 

 

Search: It is possible to select records in the table based on the values of particular attributes. If, 

for example we wanted to know how many countries were landlocked, we would use the 

“Search” function to do this. Type “Y” (note it is case sensitive) and in the drop down menu 

select “Landlocked.” Then click on the Search button. You will notice at the top of the attribute 

table that 15 records have been selected. 

Advanced search: We are going to select the landlocked countries that use the Franc for 

currency. To do this we are going to use the “Advanced search” function. 


First, make sure that no records are selected. Then click on Advanced search. In the Search 

query builder window there are 3 separate windows namely, “Fields,” “Values,” and “SQL 

where clause.” 

In order to make our selection the first thing we need to do is select those countries that are 

landlocked. To do this double click on Landlocked in the first window, then click on the “=” sign 

and then click “Sample” button below the Values window. You will see 2 options, Y and N. 

Double click on the ‘Y.’ You should see in the SQL where clause window the phrase: 

LANDLOCKED = 'Y' 

Now, click on the word “And,” then double click CURR_TYPE, click on the “=” sign and then 

select “Sample” again. This time the list of all currencies shows in the Values window. Select 

‘CFA Franc.” Your full query should read: 

LANDLOCKED = 'Y' AND CURR_TYPE = 'CFA Franc' 

You can now click on the Test button to verify that you have entered a correct SQL query and a 

window will pop up that says 5 matching features were found. Click OK and have a look at the 

attributes of the 5 selected features (you may want to Show only selected features). 

Now run the advanced search again but instead of using And use OR. You will see that a whole 

lot more features have been selected. What do you notice about their attributes (taking note of 

currency and landlocked specifically) You can see that for advanced queries it is important to 

select the correct “operator” when joining 2 queries. And you should always check your results 

once you have run a query to see that you have results that make sense. In GIS it is easy to get 

results; you want to always be sure to have results that are meaningful in the context in which 

you wish to use them. 


Practical 6 Spatial Analysis 

Outline 

Spatial Queries 

Selecting by Feature Location 

Measurements 

Segment Length 

Distance 

Area 

Geoprocessing of Vector Data 

Intersect 

Union 

Clip 

Buffer 

Dissolve 

Geoprocessing of Raster Data 

Slope Analysis 

Aspect Analysis 

Rater Calculator 

INTRODUCTION 

Spatial analysis lies at the Core of the functionality of GIS. This is where most of the calculations are 

performed on which most decisions are made. It is through spatial analysis that patterns are discerned 

are relationships determined between objects based on their spatial relation to each other. This can 

include a single object and its location in space or multiple objects and their relation to each other. 

We will explore the various basis operations that can be performed using QGIS to determine different 

spatial relationships between objects. QGIS gives us many useful tools to carry out these calculations. 


Spatial Queries: 

When a person is working with multiple datasets (layers) it is often necessary to calculate specific 

relationships between objects in these layers. For example, it may be necessary to determine how many 

of object A occur within object B, or are within a certain distance of object B. This is done using the 

Spatial Query Plugin. This Plugin in found on the Menu Bar, under the Plugins Menu (Last Option). 

This brings up the Spatial Query Dialog Box. It looks like this: 

It has 4 different criteria: 

 

 

 

 

Select source features from: 

This is the layer from which the selection is to be made. This is known 

as the Source Layer. 

Where the Feature: 

This is where the type of calculation is selected, there are 5 options 

here. These are: 

o Crosses 

o Intersects 

o Is Disjoint 

o Touches 

o Within 

Reference Features of: 

This is where the second layer is specified. This is known as the Reference Layer. 

And use the result to: 

This specifies what is to be done with the result of the operation. Most commonly the result is 

used to create a selection in the Attribute Table of the Source Layer. 

It is important to remember that the Source Layer always refers to the layer from which you want to 

make the selection. The Reference Layer gives the terms of reference for that selection. 


Task 1: 

 

Open a new QGIS project. Add the KZN_vegetation and eThekwini_fires layers from the Spatial 

Analysis Folder. 

Now zoom to the extent of these layers. The question we will attempt to answer is: 

"How many Fires are within the Thicket Biome of KZN" 

It is not possible to run this query directly. A 2 step process is needed. 

1. Select the Thicket Biome from the KZN_vegetation layer 

2. Determine the number of Fires within this area 

In order to select the Thicket Biome, access the attribute table of the KZN_vegetation layer. Now use the 

Query function to select the records that are just "Thicket". 

In the bottom right corner, type: THICKET (in capitals) into 

the "Look For" section. Make sure that "Biome" is selected 

in the "In" section. Then click on "Search". 

Once this is done, all the records for the Thicket 

Biome will be selected and they will be 

highlighted. At the top of the Attribute Table 

there will also now be a count of the number of 

selected records. 

Once the correct records have been selected, it is now possible to perform the 

Spatial Query. 

Open the Spatial Query dialog box using the Plugins Menu on the Menu Bar. Make 

sure the following selections are made in the Spatial Query Dialog Box: 

Select source features from: ethekwini_fires 

Where the feature: Within 

Reference Features of: KZN_vegetation 

VERY IMPORTANT: make sure there is a box underneath KZN_vegetation that 

states: 23 Selected geometries, and that there is a X next to it. 


This means that only the biome we selected is being included in the calculation. 

And use the result to: Create a new Selection.Click Apply 

The Spatial Query window opens with the results of the Spatial Selection. In the Bottom left can be 

found the results. In this case the result is 84 of 323 records have been selected. It is now possible to use 

this window to define more spatial queries. It is also 

possible to base the next query on the results that 

have just been obtained from the first query. This is 

done by choosing the "remove from current 

selection" option in the "And use the result to" 

section. 

It is important to note that it is only possible to 

REMOVE newly selected records from the current 

selection after having performed a Spatial Query. 

The results of the Spatial Query can also be found in the 

Attribute Table of the Source Layer. 

Measurements 

One of the most common calculations that are performed using a GIS is the measurement of certain 

objects. These measurements can be either lengths (road segments, perimeters, boundaries) or 

distances (from one location to another). 

These calculations are performed using the measure tool. 


In order to make measurements in units of distance, it is important to make sure that the project is 

using a CRS that is in meters. The default CRS is WGS84. This is a Geographic CRS and its units are 

degrees. We need to change this CRS to one that uses meters. As the data is located in South Africa, the 

Universal Transverse Mercator (UTM) Zone 36S, with the Cape Datum will give the required CRS. 

Task 2: 

 

Open QGIS and add the eThekwini and eThekwini_Health layers from the Spatial Analysis folder. 

Note that the scale bar at the top is 

in Degrees. 

In order to change the map units to meters we must alter the Project CRS. 

 

Access the Project Properties by selecting Settings, then Project Properties from the Menu Bar. 

This brings up the Project Properties Window. Select the CRS Tab. This is where the CRS of the 

Project can be altered. To find the Universal Transverse Mercator (UTM) Zone 36S Coordinate 

Reference System with the Cape Datum, select Projected Coordinate Systems, Universal 

Transverse Mercator and scroll down till you find: Cape/UTM Zone 36S. Click on this CRS and 

then click on Apply and then OK. 

This has now changed the CRS of the project to Universal Transverse Mercator (UTM) Zone 36S, with the 

Cape Datum. Note the change on the scale bar from Degrees to Meters. 

 

As changing the CRS has moved the layers to a new location it is necessary to zoom to the new 

location. This can be done using the Zoom Full button on the Tool Bar. 


In order to measure the distance between 2 places, it is necessary to first determine where they are. In 

this example 2 health institutions will be used. The question being asked is: 

"How far is it from Umhlanga Hospital to Kingsway Hospital" 

 

 

 

 

 

 

 

 

 

 

 

Select the eThekwini_Health layer. 

Right click and select Open Attribute Layer 

In the bottom right hand corner is the basic search tool. Type Hospital into the Look For section 

and then select Category from the drop down list. 

Click on Search. This will select only the hospitals. 

Check the box in the bottom left hand corner that is marked Show Selected Only. This will 

change the display of the Attribute Table to show only the selected hospitals. 

Now manually select Kingsway Hospital and Umhlanga Hospital. Select both by using the Control 

Key. 

Now select the Measure tool. 

Make sure to click on the drop down arrow and choose Measure Line. 

Move the cursor over the map. You will notice the cursor changes to a crosshair. 

Now click on one hospital and move the cursor the other hospital. You will notice that a 

Measure Dialog Box appears. Make sure to RIGHT CLICK over the second hospital. If you left click 

QGIS will think you are measuring a segment of a longer line. We will look at this in the next 

section. 

The Measure Dialog Box has 2 sections: 

The larger window is the Segments Area. This lists each segment of the line being measured and 

its length in meters. 

The last window is the total line length in Kilometers. 

 

To end the measure session, click Close in the Measure Dialog Box. 


Now to measure along the length of a line. The example for this is to measure a part of a road. Before 

starting this exercise it is important to remove all our selections. To do this use the Deselect Features 

from All Layers Button. 

 

 

Add the eThekwini_roads Layer to the Table of 

Contents. 

Using the same technique as above, measure the 

length of the N3 Highway in eThekwini. 

It is also possible to measure the Area of a polygon feature. This is done using the same technique, but it 

is important to set the Measure Tool to measure Areas. 

Geoprocessing of Vector Data 

The Geoprocessing of Vector Data requires the use of different Geoprocessing Tools. These 

Geoprocessing Tools alter or transform a layer based on its Spatial Relationship to another layer. In QGIS 

the Target Layer, that is the layer, being altered or transformed, is known as the Input Layer and the 

layer being used for the alteration or transformation is known as the "Process" Layer, where "Process" is 

the tool that is being used. For example, when using the Clip Tool, the layer being clipped is the Input 

Layer and the layer whose boundaries are being used to give the reference terms for the clip is known as 

the Clip Layer. 


QGIS supports many different Geoprocessing Tools. In this 

exercise we will be looking at the Geoprocessing Functions: 

Intersect, Union, Clip as well as Buffer and Dissolve. All these 

tools are found under the Geoprocessing Context Menu, in 

the Vector Menu on the Menu Bar. 

 

Intersect, Union and Clip 

These are both overlay functions and they both have the same effect of Joining two layers. 

However the manner in which these layers are joined is slightly different. 

Intersect: 

This operation joins two layers, however the extent of the first 

layer is cropped to the extent of the second layer. All the 

attribute data from BOTH layers is retained in this operation. 

Union: 

This operation joins two layers, however the extent of both 

layers is retained. All the attribute data from BOTH layers is 

retained in this operation. 

Clip: 

This operation is also known as the "Cookie Cutter". In this 

operation a section of one layer is cut out based on the extent 

(boundaries) of another layer. 


Buffer and Dissolve 

Buffer: 

Often it is necessary to know what lies within a certain specific 

distance of a feature. This can be done by creating a Buffer, an 

area that is a precisely measured distance from the feature of 

interest. 

Dissolve: 

This function enables the simplification of a layer by joining 

(aggregating) features based on shared attributes. 

Task 3: 

 

 

 

Open a new QGIS Project and add the EThekwini and Health Layers from the Spatial Analysis 

folder. 

Open the Attribute Tables for both layers and have a good look at them. 

Intersect: 

Open the Intersect Window from the Geoprocessing 

Menu. 

Under the Input vector Layer select Health 

Under Intersect Layer select eThekwini 

Click on Browse and give the output shapefile an 

appropriate name. Make sure you are working in the 

correct folder. 

Click Ok. Select "Yes" when asked if you want to add the 

new layer to the TOC. 


Before 

After 

 

Union: 

Open the Union Window from the Geoprocessing 

Menu. 

Under Input Vector Layer select Health 

Under Union Layer select eThekwini 


appropriate name. Make sure you are working in the 


Click Ok. Select "Yes" when asked if you want to add 

the new layer to the TOC. 

Before 

After 

Task 4: 

Start a new QGIS project. Add the Provinces and National_Roads_SA Layers. You will notice that the 

road network is of the National Highways in South Africa. In order to get the National Highways in 

Kwazulu Natal province only it is necessary to Clip the road network to the boundary of Kwazulu Natal 

province. 


Open the Attribute Table for the Provinces layer. Select the Kwazulu Natal Province. It should 

highlight on the map. 

Clip: 

Open the Clip Window from the Geoprocessing 

Menu. 

Under Input Vector Layer select 

National_Roads_SA 

Under Clip Layer select eThekwini. Make sure 

that the "Use only selected features" box is 

checked under the Clip Layer. 


appropriate name. Make sure you are working in 

the correct folder. 

Click Ok. Select "Yes" when asked if you want to 

add the new layer to the TOC. 

Before 

After 

 

Buffer: 

In order to make calculations based on proximity to features it is often necessary to create a 

buffer of specific size around those features. This makes proximity calculations easier. In this 

example we will calculate the number of health facilities within 2km of these National Roads. 

o 

o 

o 

o 

Turn off the Provinces and 

National_Roads_SA layers. 

Zoom to the project extent. 

Add the Health layer to the 

current TOC. 

Change the CRS of the Project 

to Cape/UTM Zone36S. This is 

important as we need to 

make calculations in meters. 


o 

Open the Buffer Window from the Geoprocessing 

Menu. 

Under the Input Vector Layer select 

National_Roads_KZN. 

Leave Segments to Approximate as default. 

Set the Buffer Distance to 2000 (this is in meters, so 

2000m = 2km) 

Make sure to check the Dissolve Buffer Results box. This 

makes sure that different segments of roads that are 

being buffered end up as a single feature, not multiple 

features. Give the output shapefile an appropriate 

name. Make sure you are working in the correct folder. 

Click Ok. Select "Yes" when asked if you want to add the new layer to the TOC. 

The result of the buffer is a new 

Layer. This layer lies on top of the 

layer it was created from. 

In order to calculate the number of 

health facilities within this buffer, 

we will use the Spatial Query Plugin. 

 

 

 

 

 

 

Open the Spatial Query Plugin. 

Set Select Source Feature From to Health 

Set the Where the Feature to Within 

Set Reference Features of to your Road Buffer Layer 

Select Create New Selection 

Click Apply 


The result window shows the number 

of health facilities within 2 kilometers of 

the National Roads. 

 

Dissolve 

In this example we will use the KZN_ municipalities layer to determine the Districts in KZN. Each 

District contains more than one municipality. Thus these District names are repeated for each 

municipality in that District. We can aggregate the municipalities layer to show just these 

Districts. 

o 

o 

o 

o 

o 

o 

o 

o 

Start a new QGIS project. 

Add the KZN_municipalities 

layer. 

Open the Attribute Table of 

this layer. 

Look carefully at the 

District Field. You will 

notice that districts are 

repeated. This is because 

there is often more than 

one municipality in a district. 

Open the Dissolve Window in the 

Geoprocessing Menu. 

Set the Input Vector Layer as 

KZN_municipalities. 

Set the Dissolve Field as District. 

Give the output shapefile an appropriate 

name. Make sure you are working in the 

correct folder. Click Ok. Select "Yes" when 

asked if you want to add the new layer to the TOC. 


Open the Attribute Table of the new dissolved layer. You will notice that it has been aggregated 

(condensed) to just the districts. 

Geoprocessing of Raster Data 

Quantum GIS also supports raster based analytical functions. These are Raster Based Terrain Analysis 

and Raster Calculator. 

In Raster Based Terrain Analysis there are 4 analytical functions: Slope, Aspect, Ruggedness and Total 

Curvature generators. We will concentrate on Slope and Aspect. 

Slope is the steepness, or gradient of a slope. It shows areas of steep and shallow gradient. 

Aspect is the direction that the slope is facing. 

Both of these functions rely on the map units being in meters, hence they require a projected 

coordinate system whose units are in meters. For this exercise the Cape/UTM Zone 36S projection will 

be used. 

The Raster Geoprocessing Tools are located in the 

Plugins Menu, under Raster Based Terrain Analysis. 

The Raster Based Terrain Analysis Window houses both the Slope and Aspect functions. 


Task 5: Slope Analysis 

 

Open a new QGIS project and add the layer called elevation_UTM. This is 

a DEM of eThekwini. 

Change the CRS of both the layer and the project to Cape/UTM Zone 36S. 

 

 

 

 

 

 

 

 

 

 

Zoom to the layer extent. 

Open the Properties menu of the layer and change the Color Map to 

Psuedocolor. This is in the Style Tab of the Properties window. 

This now symbolises the layer to show the altitude differences. 

Open the Raster 

Based Terrain 

Analysis window. 

Select Slope as the 

Analysis 

Select 

elevation_UTM as 

the input layer. 

Give the output a 

name and make sure to save in the 


Select GeoTIFF as the output 

format. 

Check Add Result to Project Box 

Display the resulting image as a Psuedocolor map. 

The resulting image is a raster layer showing 

the slopes of the image. 


Task 6: Aspect Analysis 

 

 

 

 

 

 

 

 

Turn off the Slope Layer. 

Open the Raster Based 

Terrain Analysis window 

again. 

Select Aspect as the Analysis 

Select elevation_UTM as the 

input layer. 

Give the output a name and make 

sure to save in the correct folder. 

Select GeoTIFF as the output 

format. 

Check Add Result to Project Box 

Display the resulting image as a Psuedocolor map. 

The resulting image is a raster layer 

showing the aspects of the image. Each 

color represents a different direction 

(North, South, East, West etc.) 

Task 7: Raster Calculator 

The Raster Calculator enables calculations based on existing raster layers. Calculations can be performed 

on a single layer to extract specific information, or on multiple layers, using each layer a function of the 

calculation. 

 

Open a new QGIS project and add the layer called elevation_UTM. 

Change the CRS of both the layer and the project to Cape/UTM Zone 36S. 

 

 

Open the Properties menu of the layer and change the Color Map to Psuedocolor. 

To access the Raster Calculator, select Raster from the Menu Bar and select Raster Calculator. 


Active Layers in the TOC 

Mathematical Operators 

Expression Area 

In order to perform a calculation we need to setup the calculation as an expression. This is done in the 

Raster Calculation Expression Area. To build this expression we use the layers from the Raster Bands box 

and the mathematical operators. 

We are going to answer the question: "Where in eThekwini is the elevation higher than 500 meters" 

The raster calculation expression for this is: "elevation_UTM" > 500 

 

 

If we had wanted to include the 500m height, we would have used the >= sign. 

To start the expression by selecting the layer. To do this double click the elevation_UTM layer in 

the Raster Bands box. This will add it to the expression box. 

Then single click the "greater than" operator (>) 

Then type in 500. 

 

 

 

 

 

You will notice a note in the bottom left hand corner of the Raster Calculator. This note tells you 

whether or not your expression is valid. 

Make sure you give the Output layer a name and check the Add Result to Project box. 

Select GeoTIFF as the output format. 

Display the resulting image as a 

Psuedocolor map. 

The areas in Red are those that are 

higher than 500m. 


Practical 7 Mapping Malaria 

Outline 

Introduction 

Managing Disease Data 

Incidence vs Prevalence 

Thematic Mapping of Prevalence 

Interpolation of Prevalence 

Introduction 

Malaria is a vector borne disease, and is one of the largest killers in Africa. It is carried by the anopheles 

mosquito which is mobile. While their lifespan is limited and their flight ranges limited the sheer number 

of mosquitoes make a significant impact. While mosquitoes feed primarily on nectar, they require the 

iron and protein from blood in order to procreate. The Female transmits the malaria virus when she 

inserts her proboscis through the skin and injects an anti-coagulant into the victim to allow her to suck 

blood from the bite site. 

In order to target and combat Malaria, one needs to identify where the disease is located. The 

distribution of Malaria changes with time, primarily due to the presence or absence of mosquitoes. 

Hence in winter (Drier months) there is less malaria due to fewer mosquitoes. Therefore to adequately 

map the disease an understanding of the presence of the vector is required. 

The most common means of identifying where the highest prevalence of malaria is located is obtained 

from medical records where cases of malaria are treated. This can locate where the case was 

contracted, giving a general area where the disease is commonly found GIS is a useful means of mapping 

the presence and absence of a disease. 

The study of diseases is known as epidemiology. There are numerous methods of determining risk and 

distribution of disease You will look at a number of statistically based methods to show where malaria is 

located. 

John Snow is widely regarded as the father of Epidemiology, when he used the presence of cholera 

cases to pinpoint the source of the infection in London, tying it to dirty water from a pump. 

In essence you will be undertaking a similar exercise. 


In this practical you will 

undertake a number of mapping 

techniques to show the 

distribution of Malaria in 

KwaZulu-Natal Similar to what 

John Snow did in London. The 

principles learnt will apply in any 

environment or country. 

Managing Disease Data 

Before working with spatial and 

attribute data it is essential to 

understand where the dat comes 

from and what each attribute 

refers to. The main data you will 

be using is the malaria_case- 

Health_facility.shp file. This file 

list the number of malaria cases 

that could be traced back to a 

location after treatment in a health facility. A patient arrives at king Edward Hospital in Durban with 

malaria. If the individual has not travelled outside of their normal residential area the case can be 

attributed to a source within close proximity to his / her residence. How these sources are determined is 

usually linked to the size of the major settlements within each administrative area or the spatial 

closeness of settlements In the case of the data you will be using the nearest points to reported 

occurrences. These are places or settlements. 

The data contains numerous columns 

Oid_1 = Object ID (Auto Number for a spatial point) 

NOTIAREA = Notification area (The area which patient stated as their area of residence.) 

NOTIDISTMA = Notified Magisterial District 

SUMOF99_ to 08_ = The total sum of cases in each year falling within the NOTIAREA 

CORR_LOC_N = Corrected location 

LATITUDE = latitude of the place of residence 

LONGITUDE = longitude of the place of residence 

CODE = Code corresponding to the malaria area 

MAL_AREA = The name of the Malaria area 

POP01 = Population in 2001 

HOMESTEADS = The number of homesteads in the Malaria area 

POP05 = the population extracted from the Census data in 2005. Data was extracted based on the 

location of the residence point falling within a Census area. 


It is vital to understand what each field means. 

Incidence vs Prevalence 

Incidence and prevalence are different statistical measures of disease occurrence. They are often 

confused. This section shows you how to calculate both Incidence and prevalence. 

Incidence 

Incidence is refered to as the risk of becoming ill over a period of time. It measures the chance of being 

infected within an area over an extended period of time. It therefore includes time as a measure. So if 

we look at the small rural community of Monzi In Northern KwaZulu-Natal the Incidence rate will be the 

total number of infections added divided by the Total average population divided by the number of 

years of records. 

Open the Layer malaria_case-Health_facility. Open the attribute table. You need to find the record for 

“Monzi” So type”Monzi” into the “Look for box and select NOTIAREA from the drop down filed selector 

and click on Search 

You will notice that at the top of the window it notifies you One matching feature is found (1 Matching 

features) 

To See this record tick the Show selected only box This will show the Monzi Record. This shows only the 

requested record. We will use this to calculate both incidence and prevalence. 

The following is a simplified method of calculating Incidence. 

Incidence needs to take into account how many years the infected individuals contributed to the total 

infected population. So to get incidence one multiplies the number of infected by the length of time 

they have been infected within the total population So if you look at the data 


1999 (which was year 1 of the 10 year study) = 57 people 

=57 x 10 = 570 person years 

2000 = 15 =15 x 9 = 135 person years etc 

This is done for each year. At the end of the study 250 people were not infected (340 – 90) = 250 x 10 = 

2500 person years Add all these person years together to get the influence of all affected individuals per 

year 

=570+135+40+28+6+5+12+4+0+2= 802 person years 

Add the cumulative infected total person years to the total uninfected years =2500 

=802+2500=3302 person years. 

The incidence rate is the total number of infected divided by the total cumulative person years in the 

sample or study = 90/3302 = 0.027256 new cases of malaria per year per person 

In other words Incidence rate is 27 anticipated new cases per thousand people each year. 

It therefore shows anticipated risk of infection. 

Prevalence 

Prevalence is a lot simpler and is referred to as the total number of cases of malaria within the entire 

population of an area at a given point in time or over the entire period. It is the number of affected 

divided by the total population. 

So in 1999 the prevalence was 57/340 = 16.7% which is extremely high! Over 3 people in 20 had malaria. 

However we want to know what the average prevalence is over all years as prevalence varies with time 

due to availability of breeding sites etc. 

To work it out you need to add all the cases together and divide it by the total population 

The total number of cases is therefore 57+15+5+4+1+1+3+2+0+2= 90 

The average total population over this period is 340 the field Pop05 (Population from 2005) 

So if we look at the Monzi example: 

Total Prevalence of malaria within the population over the 10 year period is (90/340) x 100 =26.5% 


This tells you how wide spread Malaria is within your population. Unlike the common cold which is 

transitory in nature, Some strains of Malaria can recur within an infected individual and therefore once 

infected the infected numbers can be considered cumulative. 

Now you will calculate the prevalence for all Malaria case locations reported. You will do this by creating 

a new field in your table and updating it using the field calculator 

Make sure your malaria_case-Health_facility.shp file is in the legend. Open the attribute table and 

toggle editing on. Within the Window the icon to “New column” 

becomes active. 

Add a field called “prevalence”, Make the data type decimal 

Number (real), the width3 and the Precision 2 (this sets the with 

of the column at 3 and allows for 1 decimal place. You can add a 

comment To tell users what the column means (prevalence 

figures for Malaria 1999 – 2008) Click on OK. You will find the 

column at the end of the table 

Now you will update this 

column. 

Open the Field calculator 

using the field calculator icon. This opens the filed 

calculator. 

Within the field calculator you will have to 

construct a mathematical formula using the 

existing columns to calculate prevalence (This will 

be the sum of all infections per year e.g. 

SUMOF1999_ divided by the total population 

multiplied by 100 to get a percentage) 

You will be updating an existing field namely the 

column (field) “Prevalence” that you just dreated 

The formula to use is shown below and can be 

constructed by double clicking on each field and 

using the operators to add each one to the Expression. 

((SUMOF1999_ + SUMOF2000_ + SUMOF2001_ + SUMOF2002_ + SUMOF2003_ + 

SUMOF2004_ + SUMOF2005_ + SUMOF2006_ + SUMOF2007_ + 

SUMOF2008_)/POP05)*100 

Once complete Toggle editing off and Save changes and you will see a column 


updated with percentages of prevalence. 

Now that the prevalence data is available within your attribute table you can map the prevalence using 

thematic mapping. 

Open the Layer properties window for malaria_case-Health_facility 

Go to the Syle Tab and change the style from single symbol to graduated. Use the column Prevalence 

Change the symbol size from 2 to 3. Choose the OrRd colour ramp palette. Ensure you have 5 classes 

and change your Mode to Natural breaks (Jenks) 

Then click on th Classifybutton to 

add the palette to the Style 

window You should see the 

following: 

Click on OK and you will see the 

relative prevalence of Malaria 

with Red indicating High 

prevalence and Pale Orange as 

low prevalence. 

table with 0 prevalence. However this will 

prelude possible identification of future 

prevalence’s for removed records. You can 

also remove 0 or the lowest class from the 

prevalence classes. 

In most instances you will not be 

interested in 0 prevalence and 

will only want to show high 

prevalence. There are a number 

of ways to achieve this. The first 

is to remove all records from the 

Challenge: see if you can undertake this 

Remove the 0 -3 class. 

This thematic method is a quick and easy 

way of identifying areas with high 

prevalences. 

If you want to examine just the number of 

cases per year regardless of the number of 

people present in the sample area you can 

select the year of interest and perform a 


graduated display of them. 

Undertake a graduated Jenks 5 class thematic classification of the 1999 malaria figures. 

What differences can you see between this and the previous classification 

Interpolation 

QGIS has the option of interpolating to a 

raster surface from a series of points. It offers 

2 options (TIN) Triangular Irregular Network 

which uses a series of triangles to link points. 

And (IDW) Inverse Distance Weighting which 

uses the principle that influence of a point 

decreases as you move away from it. 

You will undertake a IDW interpolation. 

First you will load the KZN boundary file. Right 

click on the KZN layer and Zoom to Extents 

(This will ensure that the Interpolation covers 

a large enough area. 

Next you will open the interpolation tool from 

within the Plugins Drop Down menu. 

This opens the interpolation Plugin window. 

Change your input layer to: 

malaria_case-Health_facility 

Select Prevalence as your interpolation Attribute And add it to the Input layer by selecting Add 

Change the Interpolation method to IDW 


Click on Set to current extent 

Leave the other options as default 

Save the output file as Prevalence. 

This will result in a rater layer being generated. You will initially see it as a standard grey rectangle. 

To View the interpolation open the properties window for prevalence and change the Color map to 

Pseudocolor. Turn on standard deviation and set it to 2 and Click ok 


You will see an image which is primarily 

blue- green but with a concentration 

of red in the north east corner. What 

interpolation does is tries to 

extrapolate data to areas that does not 

have any data. It is a model and not 

always accurate but it allows you to see 

patterns in data. You can now make 

KZN hollow and place the boundaries 

on top of the Prevalence layer. 

General Information 

http://www.malaria.org.za/Malaria_Risk/General_Information/general_information.html 


Practical 8 Summary Practical 

Outline 

Introduction 

Determining load on Health Facilities 

Buffer 

Voronoi 

Determine which points do not have access to Health facilities 

Determining which points are at risk using Water bodies 

Determining areas of need based on Prevalence 

Determine points with limited access 

Determine where to Place Interventions 

Introduction 

This practical is designed to get the user to try and identify where the greatest need is for control 

programs or health facilities to combat Malaria and the effects of malaria. It is assumed that you are 

now proficient with QGIS. Instructions will therefore be simplistic in an attempt to challenge you. 

The data has been projected into a meters projection so you can undertake buffer operations. (Hint: 

When undertaking selections create sub-selections with which to work) 

You will be working in the Municipality that shows overall Highest Malaria prevalence in KZN from 1999 

to 2008 “Umhlabuyalingana”. 

You have at your disposal 

Roads 

Rivers 

Malaria cases 

Health facilities 

Determine load on Health Facilities 

Buffer 


Use the health facilities layer and buffer this by 10 km. (Buffer) 

This buffer indicates the travel distance cut off to a clinic. 

Use this buffer to sum the number of people within reach of the clinic. This gives you an idea of load on 

facility (Join Attributes by location) 

Voronoi 

Undertake a voronoi using the health facilities. 

Work out the number of people each Health facility needs to Accommodate based on straight line 

distance. (Join Attributes by location) 

Determine malaria points without access to Facilities 

Use the Health facilities buffer to select the malaria cases which are not within reach of a health facility. 

(points in polygon + Invert selection) 

Determine Points at Risk 

Mosquitoes need water to breed. Therefore select all remaining points within 500m of a river. (Buffer 

and points within polygon) 

Determine Prevalence 

Map the points thematically to see which have the4 highest prevalence 

Limited Access 

We return to the issue of accessibility. We are looking at targeting interventions where it is most 

needed. If a malaria point is in excess of 500m from a road, they have a more difficult time accessing 

health facilities and travel. Therefore any of the remaining points outside 500m of a road is a target. 

(Buffer, Point in polygon) 

Determine what you think is the most needy Area in terms of aid. 

Which points are left Based on prevalence where which point/s should you target with aid 

Extra input 

Buffer the Malaria layer with the 2005 Population. Those areas that have overlapping Buffers have a 

potentially higher population. Does this impact on your decision 

Undertake an interpolation to see if you can verify your Choice visually

Practical Manual - Malareo

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