Style Expressions

Demonstrates rule based styling.

To style all features in a layer in the same way, you can use a symbolizer object with literal values as shown below for the land layer. In this case, all features have the same fill color. To style features in a layer based on a feature property, an expression can be provided in a symbolizer instead of literal values. In the first populated places layer below, the circle radius is based on the scalerank property. To conditionally apply different symbolizers based on a feature property, a list of rules can be provided. Each rule can have a filter expression. If this expression evaluates to true, the rule's style is applied. A rule with else: true applies if no previous rules have applied. The populated place labels are rendered with a list of rules given to the third layer.

main.js

import Map from 'ol/Map.js';
import View from 'ol/View.js';
import GeoJSON from 'ol/format/GeoJSON.js';
import Layer from 'ol/layer/Vector.js';
import Source from 'ol/source/Vector.js';

const format = new GeoJSON();

const map = new Map({
  layers: [
    new Layer({
      background: '#1a2b39',
      source: new Source({
        url: 'https://d2ad6b4ur7yvpq.cloudfront.net/naturalearth-3.3.0/ne_110m_land.geojson',
        format,
      }),
      style: {
        'fill-color': 'darkgray',
      },
    }),
    new Layer({
      source: new Source({
        url: 'https://d2ad6b4ur7yvpq.cloudfront.net/naturalearth-3.3.0/ne_50m_populated_places_simple.geojson',
        format,
      }),
      style: {
        'circle-radius': ['get', 'scalerank'],
        'circle-fill-color': 'gray',
        'circle-stroke-color': 'white',
        'circle-stroke-width': 0.5,
      },
    }),
    new Layer({
      source: new Source({
        url: 'https://d2ad6b4ur7yvpq.cloudfront.net/naturalearth-3.3.0/ne_50m_populated_places_simple.geojson',
        format,
      }),
      declutter: true,
      style: [
        {
          filter: ['>', ['get', 'pop_max'], 10_000_000],
          style: {
            'text-value': [
              'concat',
              ['get', 'adm1name'],
              ', ',
              ['get', 'adm0name'],
            ],
            'text-font': '16px sans-serif',
            'text-fill-color': 'white',
            'text-stroke-color': 'gray',
            'text-stroke-width': 2,
          },
        },
        {
          else: true,
          filter: ['>', ['get', 'pop_max'], 5_000_000],
          style: {
            'text-value': ['get', 'nameascii'],
            'text-font': '12px sans-serif',
            'text-fill-color': 'white',
            'text-stroke-color': 'gray',
            'text-stroke-width': 2,
          },
        },
      ],
    }),
  ],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 1,
  }),
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Style Expressions</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": "style-expressions",
  "dependencies": {
    "ol": "10.5.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}