Practical Manual - Malareo

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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. QGIS for Malaria Page 26
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. QGIS for Malaria Page 27
Page 1 and 2: Introduction to Geographic Informat
Page 3 and 4: occurrences you can gain a better u
Page 5 and 6: Once in the folder, using your mous
Page 7 and 8: Map Legend You now have 2 layers lo
Page 9 and 10: Select the Identify features tool a
Page 11 and 12: 30% release it and click on Apply a
Page 13 and 14: It is important to note that althou
Page 15 and 16: Open your Identify features and exa
Page 17 and 18: Acquiring Spatial Data There are nu
Page 19 and 20: This adds the shapefile to the lege
Page 21 and 22: You will be creating a layer using
Page 23 and 24: This opens a co-ordinate reference
Page 25: Next you will create a line layer (
Page 29 and 30: If you are interested in seeing the
Page 31 and 32: PROJECT COORDINATE REFERENCE SYSTEM
Page 33 and 34: Task 1: Changing the Default CRS in
Page 35 and 36: Practical 5 Tabular Data Queries Ou
Page 37 and 38: ecords. Switching and clearing yo
Page 39 and 40: Practical 6 Spatial Analysis Outlin
Page 41 and 42: Task 1: Open a new QGIS project. A
Page 43 and 44: In order to make measurements in un
Page 45 and 46: Now to measure along the length of
Page 47 and 48: Buffer and Dissolve Buffer: Often i
Page 49 and 50: Open the Attribute Table for the Pr
Page 51 and 52: The result window shows the number
Page 53 and 54: Task 5: Slope Analysis Open a new
Page 55 and 56: Active Layers in the TOC Mathematic
Page 57 and 58: In this practical you will undertak
Page 59 and 60: 1999 (which was year 1 of the 10 ye
Page 61 and 62: updated with percentages of prevale
Page 63 and 64: Click on Set to current extent Leav
Page 65 and 66: Practical 8 Summary Practical Outli

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