Visualize population density | TrackAsia GL JS Docs

Use a variable binding expression to calculate and display population density.
<!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/trackasia-gl@1.0.5/dist/trackasia-gl.js"></script>
<link href="https://unpkg.com/trackasia-gl@1.0.5/dist/trackasia-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 trackasiagl.Map({
container: 'map', // container id
style: 'https://maps.track-asia.com/styles/v1/streets.json?key=public_key', // stylesheet location
center: [30.0222, -1.9596], // starting position [lng, lat]
zoom: 5.5
});
 
map.on('load', function () {
map.addSource('rwanda-provinces', {
'type': 'geojson',
'data': 'https://docs.track-asia.com/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>