Earthquakes Heatmap

heatmap 1 kml 9 vector 69 style 22 webgl 12

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 'ol/ol.css';
import KML from 'ol/format/KML';
import Map from 'ol/Map';
import Stamen from 'ol/source/Stamen';
import VectorSource from 'ol/source/Vector';
import View from 'ol/View';
import {Heatmap as HeatmapLayer, Tile as TileLayer} from 'ol/layer';

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 Stamen({
    layer: 'toner',
  }),
});

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

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

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

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Earthquakes Heatmap</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep@1.0.6/dist/elm-pep.js"></script>
    <!-- The lines below are only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v3/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,TextDecoder"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/3.18.3/minified.js"></script>
    <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 src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "heatmap-earthquakes",
  "dependencies": {
    "ol": "6.13.1-dev"
  },
  "devDependencies": {
    "parcel": "^2.0.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}