Marker Clustering

Page Summary

• This tutorial demonstrates how to use marker clusters to manage and display a large number of markers on a Google Map, enhancing visual clarity and performance.

• The @googlemaps/markerclusterer library is used in conjunction with the Maps JavaScript API to group nearby markers into clusters.

• Clusters automatically adjust as you zoom in and out, revealing individual markers at closer zoom levels and consolidating them into clusters at further zoom levels.

• You can customize the appearance of clusters and modify the clustering algorithm to suit your specific needs.

• The tutorial provides code samples and links to further resources for implementation and customization.

Select platform: Android iOS JavaScript

Overview

This tutorial shows you how to use marker clusters to display a large number of markers on a map. You can use the @googlemaps/markerclusterer library in combination with the Maps JavaScript API to combine markers of close proximity into clusters, and simplify the display of markers on the map.

To see how marker clustering works, view the following map.

The number on a cluster indicates how many markers it contains. Notice that as you zoom into any of the cluster locations, the number on the cluster decreases, and you begin to see the individual markers on the map. Zooming out of the map consolidates the markers into clusters again.

The following sample shows the complete code you need to create this map.

TypeScript

import { MarkerClusterer } from '@googlemaps/markerclusterer';

async function init() {
    // Request needed libraries.
    const [{ InfoWindow }, { AdvancedMarkerElement, PinElement }] =
        await Promise.all([
            google.maps.importLibrary('maps'),
            google.maps.importLibrary('marker'),
        ]);

    const mapElement =
        document.querySelector<google.maps.MapElement>('gmp-map')!;
    const innerMap = mapElement.innerMap;

    const infoWindow = new InfoWindow({
        content: '',
        disableAutoPan: true,
    });

    // Create an array of alphabetical characters used to label the markers.
    const labels = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';

    // Add some markers to the map.
    const markers = locations.map((position, i) => {
        const label = labels[i % labels.length];
        const pinGlyph = new PinElement({
            glyphText: label,
            glyphColor: 'white',
        });

        const marker = new AdvancedMarkerElement({
            position,
            content: pinGlyph,
            gmpClickable: true,
        });

        // markers can only be keyboard focusable when they have click listeners
        // open info window when marker is clicked
        marker.addEventListener('gmp-click', () => {
            const content = document.createElement('div');
            content.textContent = `${String(position.lat)}, ${String(position.lng)}`;
            infoWindow.setContent(content);

            infoWindow.open({
                anchor: marker,
                map: innerMap,
            });
        });
        return marker;
    });

    // Add a marker clusterer to manage the markers.
    new MarkerClusterer({ markers, map: innerMap });
}

const locations = [
    { lat: -31.56391, lng: 147.154312 },
    { lat: -33.718234, lng: 150.363181 },
    { lat: -33.727111, lng: 150.371124 },
    { lat: -33.848588, lng: 151.209834 },
    { lat: -33.851702, lng: 151.216968 },
    { lat: -34.671264, lng: 150.863657 },
    { lat: -35.304724, lng: 148.662905 },
    { lat: -36.817685, lng: 175.699196 },
    { lat: -36.828611, lng: 175.790222 },
    { lat: -37.75, lng: 145.116667 },
    { lat: -37.759859, lng: 145.128708 },
    { lat: -37.765015, lng: 145.133858 },
    { lat: -37.770104, lng: 145.143299 },
    { lat: -37.7737, lng: 145.145187 },
    { lat: -37.774785, lng: 145.137978 },
    { lat: -37.819616, lng: 144.968119 },
    { lat: -38.330766, lng: 144.695692 },
    { lat: -39.927193, lng: 175.053218 },
    { lat: -41.330162, lng: 174.865694 },
    { lat: -42.734358, lng: 147.439506 },
    { lat: -42.734358, lng: 147.501315 },
    { lat: -42.735258, lng: 147.438 },
    { lat: -43.999792, lng: 170.463352 },
];

void init();
index.ts

Note: Read the guide on using TypeScript and Google Maps.

JavaScript

import { MarkerClusterer } from '@googlemaps/markerclusterer';

async function init() {
    // Request needed libraries.
    const [{ InfoWindow }, { AdvancedMarkerElement, PinElement }] =
        await Promise.all([
            google.maps.importLibrary('maps'),
            google.maps.importLibrary('marker'),
        ]);

    const mapElement = document.querySelector('gmp-map');
    const innerMap = mapElement.innerMap;

    const infoWindow = new InfoWindow({
        content: '',
        disableAutoPan: true,
    });

    // Create an array of alphabetical characters used to label the markers.
    const labels = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';

    // Add some markers to the map.
    const markers = locations.map((position, i) => {
        const label = labels[i % labels.length];
        const pinGlyph = new PinElement({
            glyphText: label,
            glyphColor: 'white',
        });

        const marker = new AdvancedMarkerElement({
            position,
            content: pinGlyph,
            gmpClickable: true,
        });

        // markers can only be keyboard focusable when they have click listeners
        // open info window when marker is clicked
        marker.addEventListener('gmp-click', () => {
            const content = document.createElement('div');
            content.textContent = `${String(position.lat)}, ${String(position.lng)}`;
            infoWindow.setContent(content);

            infoWindow.open({
                anchor: marker,
                map: innerMap,
            });
        });
        return marker;
    });

    // Add a marker clusterer to manage the markers.
    new MarkerClusterer({ markers, map: innerMap });
}

const locations = [
    { lat: -31.56391, lng: 147.154312 },
    { lat: -33.718234, lng: 150.363181 },
    { lat: -33.727111, lng: 150.371124 },
    { lat: -33.848588, lng: 151.209834 },
    { lat: -33.851702, lng: 151.216968 },
    { lat: -34.671264, lng: 150.863657 },
    { lat: -35.304724, lng: 148.662905 },
    { lat: -36.817685, lng: 175.699196 },
    { lat: -36.828611, lng: 175.790222 },
    { lat: -37.75, lng: 145.116667 },
    { lat: -37.759859, lng: 145.128708 },
    { lat: -37.765015, lng: 145.133858 },
    { lat: -37.770104, lng: 145.143299 },
    { lat: -37.7737, lng: 145.145187 },
    { lat: -37.774785, lng: 145.137978 },
    { lat: -37.819616, lng: 144.968119 },
    { lat: -38.330766, lng: 144.695692 },
    { lat: -39.927193, lng: 175.053218 },
    { lat: -41.330162, lng: 174.865694 },
    { lat: -42.734358, lng: 147.439506 },
    { lat: -42.734358, lng: 147.501315 },
    { lat: -42.735258, lng: 147.438 },
    { lat: -43.999792, lng: 170.463352 },
];

void init();
index.js

CSS

html,
body {
    height: 100%;
    margin: 0;
    padding: 0;
}
style.css

HTML

<html>
    <head>
        <title>Marker Clustering</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="-28.024,140.887"
            zoom="3"
            map-id="DEMO_MAP_ID"></gmp-map>
    </body>
</html>
index.html

As an illustration, this tutorial adds a set of markers to the map using the locations array. You can use other sources to get markers for your map. For more information, read the guide to creating markers.

Add a marker clusterer

Follow these steps to add a marker clusterer:

1. Add the marker clustering library to your page or application. The library is available on NPM at @googlemaps/markerclusterer and in the repository on GitHub. Select one of the following options to install the library:

   NPM

   Install the @googlemaps/markerclusterer library using NPM.

   npm install @googlemaps/markerclusterer

   CDN

   The following script loads the library from the unpkg.com CDN.

   <script src="https://unpkg.com/@googlemaps/markerclusterer/dist/index.min.js"></script>

2. Add a marker clusterer in your app.

   The following code adds a marker clusterer to the map. Select one of the following options:

   NPM

   import { MarkerClusterer } from "@googlemaps/markerclusterer";
   
   const markerCluster = new MarkerClusterer({ markers, map });

   CDN

   When accessed with the CDN, the library is available under the markerClusterer global.

   const markerCluster = new markerClusterer.MarkerClusterer({ markers, map });

   This sample passes the markers array to the MarkerClusterer.

3. (Optional) Customize the marker clusterer to change the cluster icon appearance, clustering algorithm, or click behavior.

Customize the marker clusterer

You can customize the MarkerClusterer by passing additional options in the MarkerClustererOptions object when creating the clusterer instance:

• renderer: Controls how cluster markers are rendered on the map.
• algorithm and algorithmOptions: Controls how markers are grouped into clusters based on distance and zoom level.
• onClusterClick: Overrides the default behavior when a user clicks a cluster marker.

The following map shows markers with custom cluster icons.

Customize the cluster icon

By default, MarkerClusterer uses DefaultRenderer to create SVG cluster icons. To customize the appearance of cluster markers, pass an object that implements the Renderer interface to the renderer option.

The Renderer interface requires a render(cluster, stats, map) method that returns an AdvancedMarkerElement (or a legacy google.maps.Marker). The render method receives the following arguments:

• cluster (Cluster): Represents the group of markers, including:
  • count: The number of visible markers in the cluster.
  • position: The google.maps.LatLng center position of the cluster.
  • bounds: The google.maps.LatLngBounds of the cluster.
  • markers: The array of markers contained in the cluster.
• stats (ClusterStats): Provides statistics across all clusters in the current render cycle, such as stats.clusters.markers.mean, min, max, and sum. You can use these values to style clusters dynamically based on their relative size.
• map (google.maps.Map): The map instance.

The following example defines a custom renderer that builds a circular HTML badge for each AdvancedMarkerElement and changes its background color when the cluster marker count exceeds the average cluster size.

TypeScript

// Customize the cluster icons using a custom Renderer
    const renderer = {
        render: (
            {
                count,
                position,
            }: { count: number; position: google.maps.LatLng },
            stats: ClusterStats
        ) => {
            // Change color based on the number of markers in the cluster relative to the mean
            const isLargeCluster =
                count > Math.max(10, stats.clusters.markers.mean);
            const clusterClass = isLargeCluster
                ? 'large-cluster'
                : 'small-cluster';

            // Build the HTML content for the Advanced Marker
            const content = document.createElement('div');
            content.classList.add('custom-cluster-icon', clusterClass);
            content.textContent = String(count);

            return new AdvancedMarkerElement({
                position,
                content,
                // Adjust zIndex to be above other markers
                zIndex: 1000 + count,
            });
        },
    };

    // Add a marker clusterer to manage the markers.
    new MarkerClusterer({ markers, map: innerMap, renderer });
}
index.ts

Note: Read the guide on using TypeScript and Google Maps.

JavaScript

// Customize the cluster icons using a custom Renderer
    const renderer = {
        render: ({ count, position }, stats) => {
            // Change color based on the number of markers in the cluster relative to the mean
            const isLargeCluster =
                count > Math.max(10, stats.clusters.markers.mean);
            const clusterClass = isLargeCluster
                ? 'large-cluster'
                : 'small-cluster';

            // Build the HTML content for the Advanced Marker
            const content = document.createElement('div');
            content.classList.add('custom-cluster-icon', clusterClass);
            content.textContent = String(count);

            return new AdvancedMarkerElement({
                position,
                content,
                // Adjust zIndex to be above other markers
                zIndex: 1000 + count,
            });
        },
    };

    // Add a marker clusterer to manage the markers.
    new MarkerClusterer({ markers, map: innerMap, renderer });
}
index.js

See the complete custom renderer example

TypeScript

import { MarkerClusterer, ClusterStats } from '@googlemaps/markerclusterer';

async function init() {
    // Request needed libraries.
    const [{ InfoWindow }, { AdvancedMarkerElement, PinElement }] =
        await Promise.all([
            google.maps.importLibrary('maps'),
            google.maps.importLibrary('marker'),
        ]);

    await customElements.whenDefined('gmp-map');

    const mapElement =
        document.querySelector<google.maps.MapElement>('gmp-map')!;
    const innerMap = mapElement.innerMap;

    const infoWindow = new InfoWindow({
        content: '',
        disableAutoPan: true,
    });

    // Create an array of alphabetical characters used to label the markers.
    const labels = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';

    // Add some markers to the map.
    const markers = locations.map((position, i) => {
        const label = labels[i % labels.length];
        const pinGlyph = new PinElement({
            glyphText: label,
            glyphColor: 'white',
        });

        const marker = new AdvancedMarkerElement({
            position,
            content: pinGlyph,
            gmpClickable: true,
        });

        marker.addEventListener('gmp-click', () => {
            const content = document.createElement('div');
            content.textContent = `${String(position.lat)}, ${String(position.lng)}`;
            infoWindow.setContent(content);

            infoWindow.open({
                anchor: marker,
                map: innerMap,
            });
        });
        return marker;
    });

    // Customize the cluster icons using a custom Renderer
    const renderer = {
        render: (
            {
                count,
                position,
            }: { count: number; position: google.maps.LatLng },
            stats: ClusterStats
        ) => {
            // Change color based on the number of markers in the cluster relative to the mean
            const isLargeCluster =
                count > Math.max(10, stats.clusters.markers.mean);
            const clusterClass = isLargeCluster
                ? 'large-cluster'
                : 'small-cluster';

            // Build the HTML content for the Advanced Marker
            const content = document.createElement('div');
            content.classList.add('custom-cluster-icon', clusterClass);
            content.textContent = String(count);

            return new AdvancedMarkerElement({
                position,
                content,
                // Adjust zIndex to be above other markers
                zIndex: 1000 + count,
            });
        },
    };

    // Add a marker clusterer to manage the markers.
    new MarkerClusterer({ markers, map: innerMap, renderer });
}

const locations = [
    { lat: -31.56391, lng: 147.154312 },
    { lat: -33.718234, lng: 150.363181 },
    { lat: -33.727111, lng: 150.371124 },
    { lat: -33.848588, lng: 151.209834 },
    { lat: -33.851702, lng: 151.216968 },
    { lat: -34.671264, lng: 150.863657 },
    { lat: -35.304724, lng: 148.662905 },
    { lat: -36.817685, lng: 175.699196 },
    { lat: -36.828611, lng: 175.790222 },
    { lat: -37.75, lng: 145.116667 },
    { lat: -37.759859, lng: 145.128708 },
    { lat: -37.765015, lng: 145.133858 },
    { lat: -37.770104, lng: 145.143299 },
    { lat: -37.7737, lng: 145.145187 },
    { lat: -37.774785, lng: 145.137978 },
    { lat: -37.819616, lng: 144.968119 },
    { lat: -38.330766, lng: 144.695692 },
    { lat: -39.927193, lng: 175.053218 },
    { lat: -41.330162, lng: 174.865694 },
    { lat: -42.734358, lng: 147.439506 },
    { lat: -42.734358, lng: 147.501315 },
    { lat: -42.735258, lng: 147.438 },
    { lat: -43.999792, lng: 170.463352 },
];

void init();
index.ts

Note: Read the guide on using TypeScript and Google Maps.

JavaScript

import { MarkerClusterer } from '@googlemaps/markerclusterer';

async function init() {
    // Request needed libraries.
    const [{ InfoWindow }, { AdvancedMarkerElement, PinElement }] =
        await Promise.all([
            google.maps.importLibrary('maps'),
            google.maps.importLibrary('marker'),
        ]);

    await customElements.whenDefined('gmp-map');

    const mapElement = document.querySelector('gmp-map');
    const innerMap = mapElement.innerMap;

    const infoWindow = new InfoWindow({
        content: '',
        disableAutoPan: true,
    });

    // Create an array of alphabetical characters used to label the markers.
    const labels = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';

    // Add some markers to the map.
    const markers = locations.map((position, i) => {
        const label = labels[i % labels.length];
        const pinGlyph = new PinElement({
            glyphText: label,
            glyphColor: 'white',
        });

        const marker = new AdvancedMarkerElement({
            position,
            content: pinGlyph,
            gmpClickable: true,
        });

        marker.addEventListener('gmp-click', () => {
            const content = document.createElement('div');
            content.textContent = `${String(position.lat)}, ${String(position.lng)}`;
            infoWindow.setContent(content);

            infoWindow.open({
                anchor: marker,
                map: innerMap,
            });
        });
        return marker;
    });

    // Customize the cluster icons using a custom Renderer
    const renderer = {
        render: ({ count, position }, stats) => {
            // Change color based on the number of markers in the cluster relative to the mean
            const isLargeCluster =
                count > Math.max(10, stats.clusters.markers.mean);
            const clusterClass = isLargeCluster
                ? 'large-cluster'
                : 'small-cluster';

            // Build the HTML content for the Advanced Marker
            const content = document.createElement('div');
            content.classList.add('custom-cluster-icon', clusterClass);
            content.textContent = String(count);

            return new AdvancedMarkerElement({
                position,
                content,
                // Adjust zIndex to be above other markers
                zIndex: 1000 + count,
            });
        },
    };

    // Add a marker clusterer to manage the markers.
    new MarkerClusterer({ markers, map: innerMap, renderer });
}

const locations = [
    { lat: -31.56391, lng: 147.154312 },
    { lat: -33.718234, lng: 150.363181 },
    { lat: -33.727111, lng: 150.371124 },
    { lat: -33.848588, lng: 151.209834 },
    { lat: -33.851702, lng: 151.216968 },
    { lat: -34.671264, lng: 150.863657 },
    { lat: -35.304724, lng: 148.662905 },
    { lat: -36.817685, lng: 175.699196 },
    { lat: -36.828611, lng: 175.790222 },
    { lat: -37.75, lng: 145.116667 },
    { lat: -37.759859, lng: 145.128708 },
    { lat: -37.765015, lng: 145.133858 },
    { lat: -37.770104, lng: 145.143299 },
    { lat: -37.7737, lng: 145.145187 },
    { lat: -37.774785, lng: 145.137978 },
    { lat: -37.819616, lng: 144.968119 },
    { lat: -38.330766, lng: 144.695692 },
    { lat: -39.927193, lng: 175.053218 },
    { lat: -41.330162, lng: 174.865694 },
    { lat: -42.734358, lng: 147.439506 },
    { lat: -42.734358, lng: 147.501315 },
    { lat: -42.735258, lng: 147.438 },
    { lat: -43.999792, lng: 170.463352 },
];

void init();
index.js

CSS

html,
body,
gmp-map {
    height: 100%;
    margin: 0;
    padding: 0;
}

.custom-cluster-icon {
    width: 45px;
    height: 45px;
    border-radius: 50%;
    border: 2px solid white;
    display: flex;
    justify-content: center;
    align-items: center;
    color: white;
    font-weight: bold;
    font-size: 14px;
    font-family: sans-serif;
    box-shadow: 0 2px 6px rgba(0, 0, 0, 0.3);
}

.large-cluster {
    background-color: #ff0000;
}

.small-cluster {
    background-color: #0000ff;
}
style.css

HTML

<html>
    <head>
        <title>marker-clustering-custom</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="-28.024, 140.887"
            zoom="3"
            map-id="DEMO_MAP_ID"></gmp-map>
    </body>
</html>
index.html

For additional renderer examples, see the renderer usage demo.

Modify the clustering algorithm

By default, MarkerClusterer uses SuperClusterAlgorithm, which clusters markers using k-d trees. You can customize clustering behavior by passing an algorithm instance to the algorithm option, or by passing options for the default algorithm to algorithmOptions.

The library includes the following built-in algorithms:

• SuperClusterAlgorithm (default): Fast geospatial point clustering using k-d trees. Common options include:
  • maxZoom: The maximum zoom level at which clusters are generated (default: 16). At zoom levels above maxZoom, individual markers are displayed without clustering.
  • radius: The cluster radius in pixels (default: 60).
  • minPoints: The minimum number of markers required to form a cluster (default: 2).
• SuperClusterViewportAlgorithm: A viewport-filtered variant of SuperClusterAlgorithm that only clusters markers within the current map viewport plus a pixel padding (viewportPadding, default: 60).
• GridAlgorithm: A grid-based clustering algorithm. Common options include maxZoom (default: 16), gridSize (grid size in pixels, default: 40), and maxDistance (maximum distance in meters between a cluster center and a marker, default: 40000).
• NoopAlgorithm: Renders all markers without clustering them.

The following example configures SuperClusterAlgorithm with a custom radius and maxZoom:

import {MarkerClusterer, SuperClusterAlgorithm} from '@googlemaps/markerclusterer';

const markerCluster = new MarkerClusterer({
  map,
  markers,
  algorithm: new SuperClusterAlgorithm({
    radius: 80,
    maxZoom: 15,
  }),
});

To compare how the different algorithms behave, see the algorithm comparison demo.

Customize cluster click behavior

By default, clicking a cluster marker fits the map viewport to the bounds of the clicked cluster (map.fitBounds(cluster.bounds)). To customize what happens when a user clicks a cluster, pass a callback function to the onClusterClick option:

const markerCluster = new MarkerClusterer({
  map,
  markers,
  onClusterClick: (event, cluster, map) => {
    // Zoom in by 2 levels centered on the cluster position
    map.setCenter(cluster.position);
    map.setZoom((map.getZoom() ?? 3) + 2);
  },
});

Learn more

You can view more complex examples of marker clustering in the repository on GitHub and read the reference documentation for the library.