Edit

Clustered Features

cluster2 vector60

Example of using ol/source/Cluster.

This example shows how to do clustering on point features.

main.js
import 'ol/ol.css';
import Feature from 'ol/Feature';
import Map from 'ol/Map';
import Point from 'ol/geom/Point';
import View from 'ol/View';
import {
  Circle as CircleStyle,
  Fill,
  Stroke,
  Style,
  Text,
} from 'ol/style';
import {Cluster, OSM, Vector as VectorSource} from 'ol/source';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';

var distance = document.getElementById('distance');

var count = 20000;
var features = new Array(count);
var e = 4500000;
for (var i = 0; i < count; ++i) {
  var coordinates = [2 * e * Math.random() - e, 2 * e * Math.random() - e];
  features[i] = new Feature(new Point(coordinates));
}

var source = new VectorSource({
  features: features,
});

var clusterSource = new Cluster({
  distance: parseInt(distance.value, 10),
  source: source,
});

var styleCache = {};
var clusters = new VectorLayer({
  source: clusterSource,
  style: function (feature) {
    var size = feature.get('features').length;
    var style = styleCache[size];
    if (!style) {
      style = new Style({
        image: new CircleStyle({
          radius: 10,
          stroke: new Stroke({
            color: '#fff',
          }),
          fill: new Fill({
            color: '#3399CC',
          }),
        }),
        text: new Text({
          text: size.toString(),
          fill: new Fill({
            color: '#fff',
          }),
        }),
      });
      styleCache[size] = style;
    }
    return style;
  },
});

var raster = new TileLayer({
  source: new OSM(),
});

var map = new Map({
  layers: [raster, clusters],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});

distance.addEventListener('input', function () {
  clusterSource.setDistance(parseInt(distance.value, 10));
});
index.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Clustered Features</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <form>
      <label for="distance">cluster distance</label>
      <input id="distance" type="range" min="0" max="100" step="1" value="40"/>
    </form>
    <script src="main.js"></script>
  </body>
</html>
package.json
{
  "name": "cluster",
  "dependencies": {
    "ol": "6.5.0"
  },
  "devDependencies": {
    "parcel": "^2.0.0-beta.1"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}