This tutorial will describe how to create heat maps and use them to analyze for or delineates areas or zones where points or phemena are concentrated.
Download sample data for practice by clicking this link:
Our sample data comprises an OSM point dataset comprising populated places around the world and a polygon shapefile comprising administrative boundaries of countries in Africa. The goal of the demo is to create a heat map that will identify where settlements are concentrated on the continent.
1. Launch QGIS and load the sample dataset.
2. Next, we will select only populated places that lie within the African continent. Click on Vector – Spatial Query – Spatial Query
3. Fill the details as shown on the screenshot below. Click Apply.
4. Click on the ‘create layer with selected’ icon on the expanded window.
5. Now we create the heat map. Click on Raster – Heatmap – Heatmap
6. A. Input the point layer created from the spatial query. B. For the demo, we reduce the ‘Radius’ to 20000 from default 30000. Check the box ‘Add generated file to map. Click OK
7. by default, the heat map comes out in a black and white gradient, therefore, the whitest areas rep areas with the highest concentrations. Right Click on the layer generated and choose properties from the dropdown menu.
8. Click on Style. A. Change the color gradient to ‘white to black’. B. Check the Hue box and click the dropdown button beside Colour to select a color gradient. For the demo, we select yellow. C. Click on Transparency and increase to about 23%. Click OK
9. For the final map, we use the openlayers plugin to add a google physical map under the heat map layer. See screenshot below displaying the map. The darkest spots rep the area with the highest concentration of OSM populated places.
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