Data Layer: Event Handling

  • This example demonstrates dynamically displaying information from a data layer when the mouse hovers over a KML feature object on a Google Map.

  • It uses GeoJSON data loaded onto the map and styled with custom colors and stroke weights.

  • A mouseover event listener is added to each feature, triggering the display of a specific property ("letter") in an info box.

  • The sample includes code in TypeScript and JavaScript, along with HTML and CSS for styling and structure.

This example uses a data layer to dynamically display information about a KML feature object when under the mouse cursor.

Read the documentation.

TypeScript

let map: google.maps.Map;

async function initMap() {
    (await google.maps.importLibrary('maps')) as google.maps.MapsLibrary;

    const mapElement = document.querySelector(
        'gmp-map'
    ) as google.maps.MapElement;

    const innerMap = mapElement.innerMap;

    // Load GeoJSON.
    innerMap.data.loadGeoJson('google.json');

    // Add some style.
    innerMap.data.setStyle((feature) => {
        return /** @type {google.maps.Data.StyleOptions} */ {
            fillColor: feature.getProperty('color') as string,
            strokeWeight: 1,
        };
    });

    // Set mouseover event for each feature.
    innerMap.data.addListener('mouseover', (event) => {
        (document.getElementById('info-box') as HTMLElement).textContent =
            event.feature.getProperty('letter');
    });
}

initMap();
index.ts

JavaScript

let map;
async function initMap() {
    (await google.maps.importLibrary('maps'));
    const mapElement = document.querySelector('gmp-map');
    const innerMap = mapElement.innerMap;
    // Load GeoJSON.
    innerMap.data.loadGeoJson('google.json');
    // Add some style.
    innerMap.data.setStyle((feature) => {
        return /** @type {google.maps.Data.StyleOptions} */ {
            fillColor: feature.getProperty('color'),
            strokeWeight: 1,
        };
    });
    // Set mouseover event for each feature.
    innerMap.data.addListener('mouseover', (event) => {
        document.getElementById('info-box').textContent =
            event.feature.getProperty('letter');
    });
}
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;
}

#info-box {
    background-color: white;
    border: 1px solid black;
    bottom: 30px;
    height: 20px;
    padding: 10px;
    position: absolute;
    left: 30px;
}

style.css

HTML

<html>
    <head>
        <title>Data Layer: Event Handling</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: "weekly"});</script>
    </head>
    <body>
        <gmp-map center="-28,137" zoom="4"></gmp-map>
        <div id="info-box">?</div>
    </body>
</html>
index.html

Try Sample

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/layer-data-event
  npm i
  npm start