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Custom Map Projections

AI-generated Key Takeaways

This example demonstrates how to create a map using the Gall-Peters projection instead of the default Mercator projection.
The Gall-Peters projection provides an alternative representation of the Earth's surface.
The sample code initializes a map, sets the Gall-Peters map type, and displays latitude and longitude coordinates on mouse hover.
It also adds markers for various cities using GeoJSON data.

This example creates a map using the Gall-Peters projection, rather than the default Mercator projection.

Read the documentation.

TypeScript

// This example defines an image map type using the Gall-Peters
// projection.
// https://en.wikipedia.org/wiki/Gall%E2%80%93Peters_projection
const mapElement = document.querySelector("gmp-map") as google.maps.MapElement;
let innerMap;

async function initMap() {
  // 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.
  initGallPeters();
  innerMap.mapTypes.set("gallPeters", gallPetersMapType);
  innerMap.setMapTypeId("gallPeters");

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

  innerMap.addListener("mousemove", (event: google.maps.MapMouseEvent) => {
    coordsDiv.textContent =
      "lat: " +
      Math.round(event.latLng!.lat()) +
      ", " +
      "lng: " +
      Math.round(event.latLng!.lng());
  });

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

let gallPetersMapType;

function initGallPeters() {
  const GALL_PETERS_RANGE_X = 800;
  const GALL_PETERS_RANGE_Y = 512;

  // Fetch Gall-Peters tiles stored locally on our server.
  gallPetersMapType = new google.maps.ImageMapType({
    getTileUrl: function (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 (
        "gall-peters_" +
        zoom +
        "_" +
        x +
        "_" +
        y +
        ".png"
      );
    },
    tileSize: new google.maps.Size(GALL_PETERS_RANGE_X, GALL_PETERS_RANGE_Y),
    minZoom: 0,
    maxZoom: 1,
    name: "Gall-Peters",
  });

  // Describe the Gall-Peters projection used by these tiles.
  gallPetersMapType.projection = {
    fromLatLngToPoint: function (latLng) {
      const latRadians = (latLng.lat() * Math.PI) / 180;
      return new google.maps.Point(
        GALL_PETERS_RANGE_X * (0.5 + latLng.lng() / 360),
        GALL_PETERS_RANGE_Y * (0.5 - 0.5 * Math.sin(latRadians))
      );
    },
    fromPointToLatLng: function (point, noWrap) {
      const x = point.x / GALL_PETERS_RANGE_X;
      const y = Math.max(0, Math.min(1, point.y / GALL_PETERS_RANGE_Y));

      return new google.maps.LatLng(
        (Math.asin(1 - 2 * y) * 180) / Math.PI,
        -180 + 360 * x,
        noWrap
      );
    },
  };
}

// GeoJSON, describing the locations and names of some cities.
const cities = {
  type: "FeatureCollection",
  features: [
    {
      type: "Feature",
      geometry: { type: "Point", coordinates: [-87.65, 41.85] },
      properties: { name: "Chicago" },
    },
    {
      type: "Feature",
      geometry: { type: "Point", coordinates: [-149.9, 61.218] },
      properties: { name: "Anchorage" },
    },
    {
      type: "Feature",
      geometry: { type: "Point", coordinates: [-99.127, 19.427] },
      properties: { name: "Mexico City" },
    },
    {
      type: "Feature",
      geometry: { type: "Point", coordinates: [-0.126, 51.5] },
      properties: { name: "London" },
    },
    {
      type: "Feature",
      geometry: { type: "Point", coordinates: [28.045, -26.201] },
      properties: { name: "Johannesburg" },
    },
    {
      type: "Feature",
      geometry: { type: "Point", coordinates: [15.322, -4.325] },
      properties: { name: "Kinshasa" },
    },
    {
      type: "Feature",
      geometry: { type: "Point", coordinates: [151.207, -33.867] },
      properties: { name: "Sydney" },
    },
    {
      type: "Feature",
      geometry: { type: "Point", coordinates: [0, 0] },
      properties: { name: "0°N 0°E" },
    },
  ],
};

initMap();index.ts

JavaScript

// This example defines an image map type using the Gall-Peters
// projection.
// https://en.wikipedia.org/wiki/Gall%E2%80%93Peters_projection
const mapElement = document.querySelector("gmp-map");
let innerMap;
async function initMap() {
    // 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.
    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: " +
                Math.round(event.latLng.lat()) +
                ", " +
                "lng: " +
                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);
}
let gallPetersMapType;
function initGallPeters() {
    const GALL_PETERS_RANGE_X = 800;
    const GALL_PETERS_RANGE_Y = 512;
    // Fetch Gall-Peters tiles stored locally on our server.
    gallPetersMapType = new google.maps.ImageMapType({
        getTileUrl: function (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 ("gall-peters_" +
                zoom +
                "_" +
                x +
                "_" +
                y +
                ".png");
        },
        tileSize: new google.maps.Size(GALL_PETERS_RANGE_X, GALL_PETERS_RANGE_Y),
        minZoom: 0,
        maxZoom: 1,
        name: "Gall-Peters",
    });
    // Describe the Gall-Peters projection used by these tiles.
    gallPetersMapType.projection = {
        fromLatLngToPoint: function (latLng) {
            const latRadians = (latLng.lat() * Math.PI) / 180;
            return new google.maps.Point(GALL_PETERS_RANGE_X * (0.5 + latLng.lng() / 360), GALL_PETERS_RANGE_Y * (0.5 - 0.5 * Math.sin(latRadians)));
        },
        fromPointToLatLng: function (point, noWrap) {
            const x = point.x / GALL_PETERS_RANGE_X;
            const y = Math.max(0, Math.min(1, point.y / GALL_PETERS_RANGE_Y));
            return new google.maps.LatLng((Math.asin(1 - 2 * y) * 180) / Math.PI, -180 + 360 * x, noWrap);
        },
    };
}
// GeoJSON, describing the locations and names of some cities.
const cities = {
    type: "FeatureCollection",
    features: [
        {
            type: "Feature",
            geometry: { type: "Point", coordinates: [-87.65, 41.85] },
            properties: { name: "Chicago" },
        },
        {
            type: "Feature",
            geometry: { type: "Point", coordinates: [-149.9, 61.218] },
            properties: { name: "Anchorage" },
        },
        {
            type: "Feature",
            geometry: { type: "Point", coordinates: [-99.127, 19.427] },
            properties: { name: "Mexico City" },
        },
        {
            type: "Feature",
            geometry: { type: "Point", coordinates: [-0.126, 51.5] },
            properties: { name: "London" },
        },
        {
            type: "Feature",
            geometry: { type: "Point", coordinates: [28.045, -26.201] },
            properties: { name: "Johannesburg" },
        },
        {
            type: "Feature",
            geometry: { type: "Point", coordinates: [15.322, -4.325] },
            properties: { name: "Kinshasa" },
        },
        {
            type: "Feature",
            geometry: { type: "Point", coordinates: [151.207, -33.867] },
            properties: { name: "Sydney" },
        },
        {
            type: "Feature",
            geometry: { type: "Point", coordinates: [0, 0] },
            properties: { name: "0°N 0°E" },
        },
    ],
};
initMap();index.js

CSS

/* 
 * 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;
}
style.css

HTML

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

    <link rel="stylesheet" type="text/css" href="./style.css" />
    <script type="module" src="./index.js"></script>
    <!-- prettier-ignore -->
    <script>(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)) })
      ({ key: "AIzaSyA6myHzS10YXdcazAFalmXvDkrYCp5cLc8", v: "beta" });</script>
  </head>
  <body>
    <gmp-map center="0,0" zoom="0">
      <div id="coords" slot="control-block-start-inline-center"></div>
    </gmp-map>
  </body>
</html>index.html

Try Sample

JSFiddle.net

Clone Sample

Git and Node.js are required to run this sample locally. Follow these instructions to install Node.js and NPM. The following commands clone, install dependencies and start the sample application.

  git clone https://github.com/googlemaps-samples/js-api-samples.git
  cd samples/map-projection-simple
  npm i
  npm start