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Practical Manual - Malareo

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graduated display of them.<br />

Undertake a graduated Jenks 5 class thematic classification of the 1999 malaria figures.<br />

What differences can you see between this and the previous classification<br />

Interpolation<br />

QGIS has the option of interpolating to a<br />

raster surface from a series of points. It offers<br />

2 options (TIN) Triangular Irregular Network<br />

which uses a series of triangles to link points.<br />

And (IDW) Inverse Distance Weighting which<br />

uses the principle that influence of a point<br />

decreases as you move away from it.<br />

You will undertake a IDW interpolation.<br />

First you will load the KZN boundary file. Right<br />

click on the KZN layer and Zoom to Extents<br />

(This will ensure that the Interpolation covers<br />

a large enough area.<br />

Next you will open the interpolation tool from<br />

within the Plugins Drop Down menu.<br />

This opens the interpolation Plugin window.<br />

Change your input layer to:<br />

malaria_case-Health_facility<br />

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

Change the Interpolation method to IDW<br />

QGIS for Malaria Page 62

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