A heat map turns a cloud of points into a pattern: where crimes cluster, where customers concentrate, or where wildlife is densest. QGIS makes heat maps in minutes, but a good one needs the right settings, because the radius, the weighting and the colour ramp all change what the map says. This guide shows how to build a heat map that reveals the truth instead of hiding it.

What a Heat Map Actually Shows

A heat map uses kernel density estimation to turn discrete points into a continuous surface, showing where points cluster and where they are sparse. It does not show exact locations, it shows density, which makes it ideal for spotting patterns and terrible for finding individual points. Use a heat map when the question is where things concentrate, not where a specific thing is. If the reader needs exact locations, use a dot map instead.

Building the Heat Map in QGIS

Load your point layer, open the Layer Properties, and change the symbology from Single Symbol to Heatmap. Set the radius, which controls how far each point's influence spreads, and the weight, which lets some points count more than others. QGIS renders the result live, so you can adjust the radius and see the pattern change immediately. Export the result as a raster if you need to share it, or keep it as a styled layer in your project.

Choosing the Radius

The radius is the most important setting: too small and the map shows isolated blobs, too large and everything merges into one wash. A good starting point is a radius that covers the scale of the pattern you are looking for, such as a few hundred metres for street-level crime or several kilometres for regional disease. Test two or three radii and compare them, because the right radius reveals the pattern while the wrong one hides it.

Colour Ramps and Honesty

Use a sequential colour ramp, from transparent to a single strong colour, rather than a rainbow ramp, which implies categories that do not exist. Make low-density areas transparent so the basemap shows through, and high-density areas a strong, warm colour. Label the map clearly as a density surface, not as exact locations, because readers will otherwise misread it. A heat map that looks dramatic but misleads is worse than no map at all.

Common Mistakes to Avoid

The most common mistake is using a heat map on data with too few points, which produces noise rather than pattern. Another is ignoring the map's edge: points near the boundary lose neighbours outside the study area, which underestimates density at the edges. A third is presenting a heat map without explaining the radius and the weighting, which makes the map impossible to interpret. Document your settings in the map's notes, so the reader can judge the result.

Heat Maps and Misleading Visuals

A heat map can mislead as easily as it can inform: the radius, the colour ramp, and the weighting all change the story the map tells. A large radius smooths the data and hides the detail, while a small radius shows noise as if it were signal. The ethical mapmaker tests different settings, shows the raw points alongside the heat map, and explains the method. A heat map is a visualisation, not a photograph, and the viewer deserves to know how it was made. The most honest heat map is the one that shows its work.

Key Takeaways

- A heat map shows density, not exact locations - The radius controls the pattern: too small shows blobs, too large merges everything - Use a sequential colour ramp from transparent to one strong colour - Document your radius and weighting so the map can be interpreted

Frequently Asked Questions

How do I make a heat map in QGIS? Load a point layer, open Layer Properties, change symbology to Heatmap, and set the radius and weight. Adjust the radius live until the pattern is clear.

A heat map reveals where things concentrate. Set the radius with care, use an honest colour ramp, and label it as density, not location.