Visualize population density | UNL Map JS Docs

Use a variable binding expression to calculate and display population density.

Note

If you want to test this example, edit it in JSFiddle or CodePen and replace the "YOUR-OWN-API-KEY" and "YOUR-OWN-VPM-ID" placeholders with your actual api key and vpm id.

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Visualize population density</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
<script src="https://unpkg.com/unl-map-js@0.1.5/lib/unl-map-js.js"></script>
<link href="https://unpkg.com/unl-map-js@0.1.5/lib/unl-map-js.css" rel="stylesheet" />
<link
href="https://unpkg.com/maplibre-gl@2.1.9/dist/maplibre-gl.css"
rel="stylesheet"
/>
<style>
	body { margin: 0; padding: 0; }
	#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<div id="map"></div>
<script>
var map = new UnlSdk.Map({
container: "map", // container id
apiKey: "YOUR-OWN-API-KEY",
vpmId: "YOUR-OWN-VPM-ID",
center: [30.0222, -1.9596], // starting position [lng, lat]
zoom: 7, // starting zoom
});
 
map.on("load", function () {
map.addSource("rwanda-provinces", {
type: "geojson",
data: "https://u-n-l.github.io/unl-map-js-docs/assets/rwanda-provinces.geojson",
});
map.addLayer({
id: "rwanda-provinces",
type: "fill",
source: "rwanda-provinces",
layout: {},
paint: {
"fill-color": [
"let",
"density",
["/", ["get", "population"], ["get", "sq-km"]],
[
"interpolate",
["linear"],
["zoom"],
8,
[
"interpolate",
["linear"],
["var", "density"],
274,
["to-color", "#edf8e9"],
1551,
["to-color", "#006d2c"],
],
10,
[
"interpolate",
["linear"],
["var", "density"],
274,
["to-color", "#eff3ff"],
1551,
["to-color", "#08519c"],
],
],
],
"fill-opacity": 0.7,
},
});
});
</script>
 
</body>
</html>