Vector Label Decluttering

vector 79 decluttering 2 declutter 2 labels 3

Label decluttering on polygons.

Decluttering is used to avoid overlapping labels. The overflow: true setting on the text style makes it so labels that do not fit within the bounds of a polygon are also considered for decluttering.

main.js

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

const map = new Map({
  target: 'map',
  view: new View({
    center: fromLonLat([-100, 38.5]),
    zoom: 4,
  }),
});

const labelStyle = new Style({
  text: new Text({
    font: '12px Calibri,sans-serif',
    overflow: true,
    fill: new Fill({
      color: '#000',
    }),
    stroke: new Stroke({
      color: '#fff',
      width: 3,
    }),
  }),
});
const countryStyle = new Style({
  fill: new Fill({
    color: 'rgba(255, 255, 255, 0.6)',
  }),
  stroke: new Stroke({
    color: '#319FD3',
    width: 1,
  }),
});
const style = [countryStyle, labelStyle];

const vectorLayer = new VectorLayer({
  background: 'white',
  source: new VectorSource({
    url: 'https://openlayers.org/data/vector/us-states.json',
    format: new GeoJSON(),
  }),
  style: function (feature) {
    const label = feature.get('name').split(' ').join('\n');
    labelStyle.getText().setText(label);
    return style;
  },
  declutter: true,
});

map.addLayer(vectorLayer);

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Vector Label Decluttering</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>

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

package.json

{
  "name": "vector-label-decluttering",
  "dependencies": {
    "ol": "9.1.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}