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I am trying to create a heat map on human encroachment using the heatmap plugin of QGIS 2.2. I have no problems creating a good looking raster file using a 2 km radius but I can't find my way around the values that are created as a result. I would need values in a scale such as number of points/sq km. Can anybody help me out with this? I know it is a quite basic question but I can't seem to find a solution.

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  • It would probably help to know your inputs, and what any settings or weights are. For instance what do your points represent - individual people? Weighted population counts? – Chris W Apr 16 '15 at 21:57
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Maybe you would like to try a different way. First you can generate an empty vector grid like a fishnet (Vector > Research Tools > Vector Grid (Output Grid as Polygons!)), then you can make a spatial join (Vector > Data Management Tools > Join Attributes by Location (Take summary of intersecting features! > you will need the COUNT Field in the result shape file).

If the Cell size of the fishnet is 1 sq km (1000 m x 1000 m), the result is in the attribute field "COUNT" (Count of points/sq km). If you need a smaller cell size for the vector grid, you have to calculate the number of points/ sq km with the field calculator in a new column of the attribute table. For example, if the Cell size is 0,25 sq km (500 m x 500 m), you have to calculate the theoretical density for each cell: "COUNT" * 4 (0,25 sq km * 4 = 1 sq km).

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