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.