How to create a choropleth Map from GeoJSON
This tutorial shows how to add a styled GeoJSON overlay to the map, display a popup on click, and create a map legend. As an example data, we use countries with attributes from EUROSTAT in GeoJSON format. Download the sample data here
Copy the following code, paste it into your favorite text editor, and save it as a
YOUR_MAPTILER_API_KEY_HEREwith your actual MapTiler API key.
The next it’s up to you. You can start the map in a different place by modifying the
starting zoom, and you can change the look of the map to any of our styles, or yours, by updating the
style URL. See what’s available here.
Add event handler for map load event. You will add code to create a GeoJSON source and a vector layer in this handler.
Create GeoJSON source. The following snippet creates GeoJSON source hosted on MapTiler Cloud (check out the How to Upload GeoJSON to MapTiler Cloud tutorial). The GeoJSON used in the example contains data from Eurostat Marriage indicators dataset filtrated to just countries with some value of mean age of women at first marriage in 2019. Download the sample data here
Get the id of the first symbol layer. We want to include GeoJSON below the map labels. That means we need to know the id of the first symbol layer so we can include the GeoJSON layer before this layer.
Add the GeoJSON layer. We need to include
map.addLayerfunction to display the GeoJSON under the maps labels
Create a choropleth map based on the age attribute. Change the
fill-colorproperty of the layer.
Display a popup when clicking on the geojson layer and show the information of the age attribute.
To make our map more user friendly, we will change the cursor when hovering over a geometry in the geojson layer to indicate to the user that they can click on it.
Create a map legend.
Get more details about this tutorial on Zoomable Choropleth Map from GeoJSON with MapLibre or check out the following How-tos related to choropleth maps