Heatmap Plugin (2024)

• Activate the Heatmap plugin
• Using the Heatmap plugin
• Tutorial: Creating a Heatmap

Activate the Heatmap plugin¶

First this core plugin needs to be activated using the Plugin Manager (seeThe Plugins Dialog). After activation, the heatmap icon can be found in the Raster Toolbar, and under the Raster ‣ Heatmapmenu.

Select the menu View ‣ Toolbars ‣ Raster to show theRaster Toolbar if it is not visible.

Using the Heatmap plugin¶

Clicking the Heatmap tool button opens the Heatmap plugin dialog(see figure_heatmap_settings).

The dialog has the following options:

• Input point layer: Lists all the vector point layers in the current projectand is used to select the layer to be analysed.
• Output raster: Allows you to use the button to select the folder andfilename for the output raster the Heatmap plugin generates. A file extensionis not required.
• Output format: Selects the output format. Although all formats supportedby GDAL can be chosen, in most cases GeoTIFF is the best format to choose.
• Radius: Is used to specify the heatmap search radius (or kernel bandwidth) in metersor map units. The radius specifies the distance around a point at which the influenceof the point will be felt. Larger values result in greater smoothing, but smallervalues may show finer details and variation in point density.

When the Advanced checkbox is checked, additional optionswill be available:

• Rows and Columns: Used to change the dimensions of the output raster.These values are also linked to the Cell size X and Cell size Y values.Increasing the number of rows or columns will decrease the cell size and increase thefile size of the output file. The values in Rows and Columns are also linked, so doublingthe number of rows will automatically double the number of columns and the cell sizes willalso be halved. The geographical area of the output raster will remain the same!
• Cell size X and Cell size Y: Control the geographic size of each pixel in the outputraster. Changing these values will also change the number of Rows and Columns in the outputraster.
• Kernel shape: The kernel shape controls the rate at which the influence of a pointdecreases as the distance from the point increases. Different kernels decay atdifferent rates, so a triweight kernel gives features greater weight for distances closerto the point then the Epanechnikov kernel does. Consequently, triweight results in “sharper”hotspots, and Epanechnikov results in “smoother” hotspots. A number of standard kernel functionsare available in QGIS, which are described and illustrated on Wikipedia.
• Decay ratio: Can be used with Triangular kernels to further control how heat froma feature decreases with distance from the feature.
  • A value of 0 (=minimum) indicates that the heat will be concentrated in the centre of thegiven radius and completely extinguished at the edge.
  • A value of 0.5 indicates that pixels at the edge of the radius will be given half the heatas pixels at the centre of the search radius.
  • A value of 1 means the heat is spread evenly over the whole search radius circle. (Thisis equivalent to the ‘Uniform’ kernel.)
  • A value greater than 1 indicates that the heat is higher towards the edge of the search radiusthan at the centre.

The input point layer may also have attribute fields which can affect how they influencethe heatmap:

• Use radius from field: Sets the search radius for each feature from an attribute field in the input layer.
• Use weight from field: Allows input features to be weighted by an attribute field. This can be used toincrease the influence certain features have on the resultant heatmap.

When an output raster file name is specified, the [OK] button can be used to create theheatmap.

Tutorial: Creating a Heatmap¶

For the following example, we will use the airports vector point layer fromthe QGIS sample dataset (see Sample Data). Another excellent QGIStutorial on making heatmaps can be found at http://www.qgistutorials.com.

In Figure_Heatmap_data, the airports of Alaska are shown.

1. Select the Heatmap tool button to open the Heatmap dialog(see Figure_Heatmap_settings).
2. In the Input point layer field, select airportsfrom the list of point layers loaded in the current project.
3. Specify an output filename by clicking the button next to theOutput raster field. Enter the filename heatmap_airports (nofile extension is necessary).
4. Leave the Output format as the default format, GeoTIFF.
5. Change the Radius to 1000000 meters.
6. Click on [OK] to create and load the airports heatmap (see Figure_Heatmap_created).

QGIS will generate the heatmap and add the results to your map window. By default, the heatmapis shaded in greyscale, with lighter areas showing higher concentrations of airports. The heatmapcan now be styled in QGIS to improve its appearance.

1. Open the properties dialog of the heatmap_airports layer (select the layerheatmap_airports, open the context menu with the right mouse button and selectProperties).
2. Select the Style tab.
3. Change the Render type to ‘Singleband pseudocolor’.
4. Select a suitable Color map , for instance YlOrRed.
5. Click the [Load] button to fetch the minimum and maximum values from the raster,then click the [Classify] button.
6. Press [OK] to update the layer.

The final result is shown in Figure_Heatmap_styled.