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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

async function init() {
    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 {
            fillColor: feature.getProperty('color') as string,
            strokeWeight: 1,
        };
    });

    // Set mouseover event for each feature.
    innerMap.data.addListener(
        'mouseover',
        (event: google.maps.Data.MouseEvent) => {
            document.getElementById('info-box')!.textContent =
                event.feature.getProperty('letter') as string;
        }
    );
}

void init();index.ts

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

JavaScript

async function init() {
    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 {
            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');
    });
}

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;
}

#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>
        <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="-28,137" zoom="4"></gmp-map>
        <div id="info-box">?</div>
    </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. 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

Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.

Last updated 2026-08-26 UTC.

Need to tell us more? [[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2026-08-26 UTC."],[],["This code dynamically displays KML feature information on a Google Map using a data layer. It initializes a map, loads GeoJSON data, and styles features based on their \"color\" property. A mouseover event listener is added to each feature, updating an \"info-box\" element with the feature's \"letter\" property when the cursor is over it. CSS styles the map and info box. HTML structures the page with the map and info box elements and load the Javascript and the google maps API.\n"]]

Data Layer: Event Handling Stay organized with collections Save and categorize content based on your preferences.

Page Summary

TypeScript

JavaScript

CSS

HTML

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