Map Export

Export a map as a PNG image.

Example of exporting a map as a PNG image, using a HTMLCanvasElement as temporary map target.

main.js

import Map from 'ol/Map.js';
import View from 'ol/View.js';
import {asArray} from 'ol/color.js';
import GeoJSON from 'ol/format/GeoJSON.js';
import HeatmapLayer from 'ol/layer/Heatmap.js';
import VectorLayer from 'ol/layer/Vector.js';
import VectorSource from 'ol/source/Vector.js';
import Fill from 'ol/style/Fill.js';
import Style from 'ol/style/Style.js';

const style = new Style({
  fill: new Fill({
    color: '#eeeeee',
  }),
});

const map = new Map({
  layers: [
    new VectorLayer({
      source: new VectorSource({
        url: 'https://openlayers.org/data/vector/ecoregions.json',
        format: new GeoJSON(),
      }),
      background: 'white',
      style: function (feature) {
        const color = asArray(feature.get('COLOR_NNH') || '#eeeeee');
        color[3] = 0.75;
        style.getFill().setColor(color);
        return style;
      },
    }),
    new HeatmapLayer({
      source: new VectorSource({
        url: 'data/geojson/world-cities.geojson',
        format: new GeoJSON(),
      }),
      weight: function (feature) {
        return feature.get('population') / 1e7;
      },
      radius: 15,
      blur: 15,
      opacity: 0.75,
    }),
  ],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});

document.getElementById('export-png').addEventListener('click', () => {
  const mapCanvas = document.createElement('canvas');
  const size = map.getSize();
  mapCanvas.width = size[0];
  mapCanvas.height = size[1];
  map.once('rendercomplete', () => {
    map.setTarget('map');
    const link = document.getElementById('image-download');
    link.href = mapCanvas.toDataURL();
    link.click();
  });
  map.setTarget(mapCanvas);
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Map Export</title>
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css">
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@fortawesome/[email protected]/css/fontawesome.min.css">
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@fortawesome/[email protected]/css/solid.css">
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <a id="export-png" class="btn btn-outline-dark" role="button"><i class="fa fa-download"></i> Download PNG</a>
    <a id="image-download" download="map.png"></a>

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

package.json

{
  "name": "export-map",
  "dependencies": {
    "ol": "10.7.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}