Practical Manual - Malareo

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<strong>Practical</strong> 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). QGIS for Malaria Page 30
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: QGIS for Malaria Page 31
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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 and 26: Next you will create a line layer (
Page 27 and 28: Continue digitising the other roads
Page 29: If you are interested in seeing the
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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