Vector Image Layer

Example of rendering vector data as an image layer.

This example uses ol/layer/VectorImage for faster rendering during interaction and animations, at the cost of less accurate rendering.

main.js

import 'ol/ol.css';
import GeoJSON from 'ol/format/GeoJSON';
import Map from 'ol/Map';
import VectorImageLayer from 'ol/layer/VectorImage';
import VectorLayer from 'ol/layer/Vector';
import VectorSource from 'ol/source/Vector';
import View from 'ol/View';
import {Fill, Stroke, Style, Text} from 'ol/style';

const style = new Style({
  fill: new Fill({
    color: 'rgba(255, 255, 255, 0.6)',
  }),
  stroke: new Stroke({
    color: '#319FD3',
    width: 1,
  }),
  text: new Text(),
});

const map = new Map({
  layers: [
    new VectorImageLayer({
      imageRatio: 2,
      source: new VectorSource({
        url: 'data/geojson/countries.geojson',
        format: new GeoJSON(),
      }),
      style: function (feature) {
        style.getText().setText(feature.get('name'));
        return style;
      },
    }),
  ],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 1,
  }),
});

const featureOverlay = new VectorLayer({
  source: new VectorSource(),
  map: map,
  style: new Style({
    stroke: new Stroke({
      color: '#f00',
      width: 1,
    }),
    fill: new Fill({
      color: 'rgba(255,0,0,0.1)',
    }),
  }),
});

let highlight;
const displayFeatureInfo = function (pixel) {
  map
    .getLayers()
    .item(0)
    .getFeatures(pixel)
    .then(function (features) {
      const feature = features.length > 0 ? features[0] : undefined;

      const info = document.getElementById('info');
      if (feature) {
        info.innerHTML = feature.getId() + ': ' + feature.get('name');
      } else {
        info.innerHTML = '&nbsp;';
      }

      if (feature !== highlight) {
        if (highlight) {
          featureOverlay.getSource().removeFeature(highlight);
        }
        if (feature) {
          featureOverlay.getSource().addFeature(feature);
        }
        highlight = feature;
      }
    });
};

map.on('pointermove', function (evt) {
  if (!evt.dragging) {
    displayFeatureInfo(evt.pixel);
  }
});

map.on('click', function (evt) {
  displayFeatureInfo(evt.pixel);
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Vector Image Layer</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep"></script>
    <!-- The line below is 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,URL,TextDecoder,Number.isInteger"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div id="info">&nbsp;</div>
    <script src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "image-vector-layer",
  "dependencies": {
    "ol": "6.6.1"
  },
  "devDependencies": {
    "parcel": "^2.0.0-beta.1"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}