Heatmaps

Heatmaps are useful to show intensity or frequency of occurrence. Heatmaps can be thought about as generalized dot density maps.

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Making a heatmap

1 Add the layer chestnut-trees.geojson from the thematic mapping subfolder to your QGIS project.

As it is, this is a dot density map. Now let’s make it into a heatmap to accentuate areas where there are more chestnut street trees.

2 Open the Layer Properties and go to Symbology. Change the symbolization to Heatmap.

3 Choose an appropriate color ramp. Then, click on the color ramp itself in order to adjust Color 1. Set the Opacity of Color 1 to be 0. In other words, make the lighter/lower end of the color ramp totally transparent. This will ensure that areas that have no value are see-through, and don’t hide the map.

3 Radius has to do with how far around the points the color blurs. 8-12 works well. I also recommend adjusting the Rendering Quality all the way to Best, otherwise, the heatmap becomes quite pixelated.