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I would like to make a heat map of "building density" based on the area of the building footprints (I have them in a geojson as polygons) in relation to their "non-building" surroundings based on fixed grid (or alternative). So in other words put a grid over the map 100x100m and in each grid sector look at the area relatioship between the building footprint and the surrounding footprint. The more building the denser.

How would I best go about this? Are there better ways to do area based heatmaps? I have calculated centroids for each building and made heat maps with that but I need something based on area not topology.

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One approach is to convert your polygons to binary raster and calculate the percent building cover within a moving (focal) window for each pixel. Here is how:

  1. Convert the vector polygon building footprints to binary raster where building = 1, else 0.

    Raster > Conversion > Rasterize (Vector to Raster)

enter image description here

  1. Run a moving window using some areal unit that is meaningful (e.g. 100m^2, acres, miles^2, etc.) with a mean statistic to calculate percent building cover per unit area.

    Processing Toolbox > GRASS > Raster > r.neighbors

enter image description here

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    Thank you so much, this is perfect! – kermitt Sep 2 '20 at 16:13
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    This worked nicely. For anyone experiencing issues with step 1: make sure your vector layer has the same projection set as the crs in the project properties. I exported the layer with the right projection and reinserted it. This resolved any issues. (changing the projection settings in the layer did not). – kermitt Sep 2 '20 at 17:51

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