Mapping Density with Hexagonal Grids

A very common approach for mapping point density is to use heat maps. If you are aiming for a different style, give hexagonal grids a try. The workflow is very simple in QGIS:

1. Load the point layer
2. Create a hexagonal grid using MMQGIS – Create Grid Layer
3. Count points per polygon (Vector menu)

I’ve applied this method to an OGD dataset of the Viennese tree cadastre containing 119,744 tree positions:

Rendering tree counts per hexagonal grid cell reveals some of Vienna’s greenest spots, such as the Prater or Türkenschanzpark.

There’s also a printable version.

Some notes on the necessary steps:

MMQGIS – Create Grid Layer performs great. Creating the 18,400 hexagons in this map was very fast. Note though, that this tool doesn’t seem to write correct projection information to the resulting Shapefile. Therefore it is necessary to set the projection manually after loading the file.

As a result, it is very likely that the Points in Polygon tool will warn you that the point and polygon layer are not in the same projection. I ignored the warning and everything went fine. This step was reasonably fast considering the number of points (119,744) and polygons (18,400).