This example uses OpenLayers v10.9.0. The latest is v.
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#### Earthquakes Heatmap

heatmap 2 kml 9 vector 86 style 27 webgl 18

#####

radius size blur size

Demonstrates the use of a heatmap layer.

This example parses a KML file and renders the features as a `ol/layer/Heatmap` layer.

##### main.js

    import Map from 'ol/Map.js';
    import View from 'ol/View.js';
    import KML from 'ol/format/KML.js';
    import HeatmapLayer from 'ol/layer/Heatmap.js';
    import TileLayer from 'ol/layer/Tile.js';
    import StadiaMaps from 'ol/source/StadiaMaps.js';
    import VectorSource from 'ol/source/Vector.js';

    const blur = document.getElementById('blur');
    const radius = document.getElementById('radius');

    const vector = new HeatmapLayer({
      source: new VectorSource({
        url: 'data/kml/2012_Earthquakes_Mag5.kml',
        format: new KML({
          extractStyles: false,
        }),
      }),
      blur: parseInt(blur.value, 10),
      radius: parseInt(radius.value, 10),
      weight: function (feature) {
        // 2012_Earthquakes_Mag5.kml stores the magnitude of each earthquake in a
        // standards-violating <magnitude> tag in each Placemark.  We extract it from
        // the Placemark's name instead.
        const name = feature.get('name');
        const magnitude = parseFloat(name.substr(2));
        return magnitude - 5;
      },
    });

    const raster = new TileLayer({
      source: new StadiaMaps({
        layer: 'stamen_toner',
      }),
    });

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

    blur.addEventListener('input', function () {
      vector.setBlur(parseInt(blur.value, 10));
    });

    radius.addEventListener('input', function () {
      vector.setRadius(parseInt(radius.value, 10));
    });

##### index.html

    <!DOCTYPE html>
    <html lang="en">
      <head>
        <meta charset="UTF-8">
        <title>Earthquakes Heatmap</title>
        <link rel="stylesheet" href="node_modules/ol/ol.css">
        <style>
          .map {
            width: 100%;
            height: 400px;
          }
        </style>
      </head>
      <body>
        <div id="map" class="map"></div>
        <form>
          <label for="radius">radius size</label>
          <input id="radius" type="range" min="1" max="50" step="1" value="5"/>
          <label for="blur">blur size</label>
          <input id="blur" type="range" min="1" max="50" step="1" value="15"/>
        </form>

        <script type="module" src="main.js"></script>
      </body>
    </html>

##### package.json

    {
      "name": "heatmap-earthquakes",
      "dependencies": {
        "ol": "10.9.0"
      },
      "devDependencies": {
        "vite": "^3.2.3"
      },
      "scripts": {
        "start": "vite",
        "build": "vite build"
      }
    }