Display HTML clusters with custom properties | NMaps GL JS Docs

This advanced example uses NMaps GL JS clustering with HTML markers and custom property expressions number-format, get, !=, >, >=, all, and case.
To use HTML or SVG for clusters in place of a NMaps GL layer, you have to manually synchronize the clustered source with a pool of marker objects that updates continuously while the map view changes.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Display HTML clusters with custom properties</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
<script src="https://cdn.ndrive.com/nmapsgl/v1.6.6/nmaps-gl.js"></script>
<link href="https://cdn.ndrive.com/nmapsgl/v1.6.6/nmaps-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>
	// TO MAKE THE MAP APPEAR YOU MUST ADD YOUR ACCESS TOKEN
	nmapsgl.accessToken = '<your access token here>';
	
const map = new nmapsgl.Map({
container: 'map',
zoom: 0.3,
center: [0, 20],
style: 'Streets'
});
 
map.addControl(new nmapsgl.NavigationControl());
 
// filters for classifying earthquakes into five categories based on magnitude
const mag1 = ['<', ['get', 'mag'], 2];
const mag2 = ['all', ['>=', ['get', 'mag'], 2], ['<', ['get', 'mag'], 3]];
const mag3 = ['all', ['>=', ['get', 'mag'], 3], ['<', ['get', 'mag'], 4]];
const mag4 = ['all', ['>=', ['get', 'mag'], 4], ['<', ['get', 'mag'], 5]];
const mag5 = ['>=', ['get', 'mag'], 5];
 
// colors to use for the categories
const colors = ['#fed976', '#feb24c', '#fd8d3c', '#fc4e2a', '#e31a1c'];
 
map.on('load', () => {
// add a clustered GeoJSON source for a sample set of earthquakes
map.addSource('earthquakes', {
'type': 'geojson',
'data': 'https://nmaps-gl.ndrive.com/nmaps-gl-js/assets/earthquakes.geojson',
'cluster': true,
'clusterRadius': 80,
'clusterProperties': {
// keep separate counts for each magnitude category in a cluster
'mag1': ['+', ['case', mag1, 1, 0]],
'mag2': ['+', ['case', mag2, 1, 0]],
'mag3': ['+', ['case', mag3, 1, 0]],
'mag4': ['+', ['case', mag4, 1, 0]],
'mag5': ['+', ['case', mag5, 1, 0]]
}
});
// circle and symbol layers for rendering individual earthquakes (unclustered points)
map.addLayer({
'id': 'earthquake_circle',
'type': 'circle',
'source': 'earthquakes',
'filter': ['!=', 'cluster', true],
'paint': {
'circle-color': [
'case',
mag1,
colors[0],
mag2,
colors[1],
mag3,
colors[2],
mag4,
colors[3],
colors[4]
],
'circle-opacity': 0.6,
'circle-radius': 12
}
});
map.addLayer({
'id': 'earthquake_label',
'type': 'symbol',
'source': 'earthquakes',
'filter': ['!=', 'cluster', true],
'layout': {
'text-field': [
'number-format',
['get', 'mag'],
{ 'min-fraction-digits': 1, 'max-fraction-digits': 1 }
],
'text-font': ['Open Sans Regular'],
'text-size': 10
},
'paint': {
'text-color': [
'case',
['<', ['get', 'mag'], 3],
'black',
'white'
]
}
});
 
// objects for caching and keeping track of HTML marker objects (for performance)
const markers = {};
let markersOnScreen = {};
 
function updateMarkers() {
const newMarkers = {};
const features = map.querySourceFeatures('earthquakes');
 
// for every cluster on the screen, create an HTML marker for it (if we didn't yet),
// and add it to the map if it's not there already
for (let i = 0; i < features.length; i++) {
const coords = features[i].geometry.coordinates;
const props = features[i].properties;
if (!props.cluster) continue;
let id = props.cluster_id;
 
let marker = markers[id];
if (!marker) {
const el = createDonutChart(props);
marker = markers[id] = new nmapsgl.Marker({
element: el
}).setLngLat(coords);
}
newMarkers[id] = marker;
 
if (!markersOnScreen[id]) marker.addTo(map);
}
// for every marker we've added previously, remove those that are no longer visible
for (let id in markersOnScreen) {
if (!newMarkers[id]) markersOnScreen[id].remove();
}
markersOnScreen = newMarkers;
}
 
// after the GeoJSON data is loaded, update markers on the screen and do so on every map move/moveend
map.on('data', (e) => {
if (e.sourceId !== 'earthquakes' || !e.isSourceLoaded) return;
 
map.on('move', updateMarkers);
map.on('moveend', updateMarkers);
updateMarkers();
});
});
 
// code for creating an SVG donut chart from feature properties
function createDonutChart(props) {
const offsets = [];
const counts = [
props.mag1,
props.mag2,
props.mag3,
props.mag4,
props.mag5
];
let total = 0;
for (let i = 0; i < counts.length; i++) {
offsets.push(total);
total += counts[i];
}
const fontSize =
total >= 1000 ? 22 : total >= 100 ? 20 : total >= 10 ? 18 : 16;
const r =
total >= 1000 ? 50 : total >= 100 ? 32 : total >= 10 ? 24 : 18;
const r0 = Math.round(r * 0.6);
const w = r * 2;
 
let html =
'<div><svg width="' +
w +
'" height="' +
w +
'" viewbox="0 0 ' +
w +
' ' +
w +
'" text-anchor="middle" style="font: ' +
fontSize +
'px sans-serif; display: block">';
 
for (let i = 0; i < counts.length; i++) {
html += donutSegment(
offsets[i] / total,
(offsets[i] + counts[i]) / total,
r,
r0,
colors[i]
);
}
html +=
'<circle cx="' +
r +
'" cy="' +
r +
'" r="' +
r0 +
'" fill="white" /><text dominant-baseline="central" transform="translate(' +
r +
', ' +
r +
')">' +
total.toLocaleString() +
'</text></svg></div>';
 
const el = document.createElement('div');
el.innerHTML = html;
return el.firstChild;
}
 
function donutSegment(start, end, r, r0, color) {
if (end - start === 1) end -= 0.00001;
const a0 = 2 * Math.PI * (start - 0.25);
const a1 = 2 * Math.PI * (end - 0.25);
const x0 = Math.cos(a0),
y0 = Math.sin(a0);
const x1 = Math.cos(a1),
y1 = Math.sin(a1);
const largeArc = end - start > 0.5 ? 1 : 0;
 
return [
'<path d="M',
r + r0 * x0,
r + r0 * y0,
'L',
r + r * x0,
r + r * y0,
'A',
r,
r,
0,
largeArc,
1,
r + r * x1,
r + r * y1,
'L',
r + r0 * x1,
r + r0 * y1,
'A',
r0,
r0,
0,
largeArc,
0,
r + r0 * x0,
r + r0 * y0,
'" fill="' + color + '" />'
].join(' ');
}
</script>
 
</body>
</html>