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Custom Map Projections

Page Summary

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')!;
let innerMap: google.maps.Map;

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: google.maps.MapMouseEvent) => {
        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') as string,
            optimized: false,
        };
    });
    innerMap.data.addGeoJson(cities);
}

async function initGallPeters(): Promise<google.maps.ImageMapType> {
    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 `gall-peters_${String(zoom)}_${String(x)}_${String(y)}.png`;
        },
        tileSize: new 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(latLng: google.maps.LatLng) {
            const latRadians = (latLng.lat() * Math.PI) / 180;
            return new Point(
                GALL_PETERS_RANGE_X * (0.5 + latLng.lng() / 360),
                GALL_PETERS_RANGE_Y * (0.5 - 0.5 * Math.sin(latRadians))
            );
        },
        fromPointToLatLng(point: google.maps.Point, noWrap?: boolean) {
            const x = point.x / GALL_PETERS_RANGE_X;
            const y = Math.max(0, Math.min(1, point.y / GALL_PETERS_RANGE_Y));

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

    return gallPetersMapType;
}

// 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' },
        },
    ],
};

void init();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 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 `gall-peters_${String(zoom)}_${String(x)}_${String(y)}.png`;
        },
        tileSize: new 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(latLng) {
            const latRadians = (latLng.lat() * Math.PI) / 180;
            return new Point(
                GALL_PETERS_RANGE_X * (0.5 + latLng.lng() / 360),
                GALL_PETERS_RANGE_Y * (0.5 - 0.5 * Math.sin(latRadians))
            );
        },
        fromPointToLatLng(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 LatLng(
                (Math.asin(1 - 2 * y) * 180) / Math.PI,
                -180 + 360 * x,
                noWrap
            );
        },
    };

    return gallPetersMapType;
}

// 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' },
        },
    ],
};

void init();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>
        <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))})({
                key: "GOOGLE_MAPS_API_KEY" 
            });
        </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

Clone Sample

Git and Node.js are required to run this sample locally. Follow these instructions to install Node.js and NPM. You will also need a Google Maps API key.

The following commands clone the repository, install dependencies, and copy the environment file.

  git clone https://github.com/googlemaps-samples/js-api-samples.git
  cd js-api-samples
  npm i
  cp .env.template .env

Once you copy the environment file, make sure to open the .env file and replace <Insert your own development API key here> with your actual API key before starting the sample.

  cd samples/map-projection-simple
  npm start