map-projection-simple

Sample code supporting Google Maps Platform JavaScript API documentation. author(s): Geo Developer IX Documentation Team

HTML

<!doctype html>
<!--
 @license
 Copyright 2026 Google LLC. All Rights Reserved.
 SPDX-License-Identifier: Apache-2.0
-->

<html>
  <head>
    <title>Custom Map Projections</title>

    <script>
      // prettier-ignore
      (g=>{var h,a,k,p="The Google Maps JavaScript API",c="google",l="importLibrary",q="__ib__",m=document,b=window;b=b[c]||(b[c]={});var d=b.maps||(b.maps={}),r=new Set,e=new URLSearchParams,u=()=>h||(h=new Promise(async(f,n)=>{await (a=m.createElement("script"));e.set("libraries",[...r]+"");for(k in g)e.set(k.replace(/[A-Z]/g,t=>"_"+t[0].toLowerCase()),g[k]);e.set("callback",c+".maps."+q);a.src=`https://maps.${c}apis.com/maps/api/js?`+e;d[q]=f;a.onerror=()=>h=n(Error(p+" could not load."));a.nonce=m.querySelector("script[nonce]")?.nonce||"";m.head.append(a)}));d[l]?console.warn(p+" only loads once. Ignoring:",g):d[l]=(f,...n)=>r.add(f)&&u().then(()=>d[l](f,...n))})({
            });
    </script>
  </head>
  <body>
    <gmp-map center="0,0" zoom="0">
      <div id="coords" slot="control-block-start-inline-center"></div>
    </gmp-map>
  </body>
</html>

CSS

/**
 * @license
 * Copyright 2026 Google LLC. All Rights Reserved.
 * SPDX-License-Identifier: Apache-2.0
 */

/* 
 * Always set the map height explicitly to define the size of the div element
 * that contains the map. 
 */
#map {
  height: 100%;
}

/* 
 * Optional: Makes the sample page fill the window. 
 */
html,
body {
  height: 100%;
  margin: 0;
  padding: 0;
}

#coords {
  background-color: black;
  color: white;
  padding: 5px;
}

JavaScript

/**
 * @license
 * Copyright 2026 Google LLC. All Rights Reserved.
 * SPDX-License-Identifier: Apache-2.0
 */

// This example defines an image map type using the Gall-Peters
// projection.
// https://en.wikipedia.org/wiki/Gall%E2%80%93Peters_projection
const ASSET_BASE_URL = new URL(
  'https://maps-docs-team.web.app/samples/map-projection-simple/dist/'
);
const mapElement = document.querySelector('gmp-map');
let innerMap;

async function init() {
  // Request the needed libraries.
  await google.maps.importLibrary('maps');

  // Create a map.
  innerMap = mapElement.innerMap;
  innerMap.setOptions({
    mapTypeControl: false,
  });

  // Set the Gall-Peters map type.
  const gallPetersMapType = await initGallPeters();
  innerMap.mapTypes.set('gallPeters', gallPetersMapType);
  innerMap.setMapTypeId('gallPeters');

  // Show the lat and lng under the mouse cursor.
  const coordsDiv = document.getElementById('coords');

  innerMap.addListener('mousemove', (event) => {
    coordsDiv.textContent = `lat: ${String(Math.round(event.latLng.lat()))}, lng: ${String(Math.round(event.latLng.lng()))}`;
  });

  // Add some markers to the map.
  innerMap.data.setStyle((feature) => {
    return {
      title: feature.getProperty('name'),
      optimized: false,
    };
  });
  innerMap.data.addGeoJson(cities);
}

async function initGallPeters() {
  const [{ ImageMapType }, { Size, Point, LatLng }] = await Promise.all([
    google.maps.importLibrary('maps'),
    google.maps.importLibrary('core'),
  ]);

  const GALL_PETERS_RANGE_X = 800;
  const GALL_PETERS_RANGE_Y = 512;

  // Fetch Gall-Peters tiles stored locally on our server.
  const gallPetersMapType = new ImageMapType({
    getTileUrl(coord, zoom) {
      const scale = 1 << zoom;

      // Wrap tiles horizontally.
      const x = ((coord.x % scale) + scale) % scale;

      // Don't wrap tiles vertically.
      const y = coord.y;

      if (y < 0 || y >= scale) return '';

      return new URL(
       ...