Customizing a Google Map: Custom Legends

Overview

Learn how to create a legend on a Google map through this tutorial. Legends generally describe the symbols and markers on a map. You can create them using the positioning feature of custom controls.

The map below contains a legend that provides information about three different custom markers on the map.

The section below displays the entire code you need to create the map and legend in this tutorial.

TypeScript

let map: google.maps.Map;

function initMap(): void {
  map = new google.maps.Map(document.getElementById("map") as HTMLElement, {
    zoom: 16,
    center: new google.maps.LatLng(-33.91722, 151.23064),
    mapTypeId: "roadmap",
  });

  const iconBase = "https://maps.google.com/mapfiles/kml/shapes/";
  const icons: Record<string, any> = {
    parking: {
      name: "Parking",
      icon: iconBase + "parking_lot_maps.png",
    },
    library: {
      name: "Library",
      icon: iconBase + "library_maps.png",
    },
    info: {
      name: "Info",
      icon: iconBase + "info-i_maps.png",
    },
  };

  const features = [
    {
      position: new google.maps.LatLng(-33.91721, 151.2263),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91539, 151.2282),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91747, 151.22912),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.9191, 151.22907),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91725, 151.23011),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91872, 151.23089),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91784, 151.23094),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91682, 151.23149),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.9179, 151.23463),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91666, 151.23468),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.916988, 151.23364),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91662347903106, 151.22879464019775),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.916365282092855, 151.22937399734496),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.91665018901448, 151.2282474695587),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.919543720969806, 151.23112279762267),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.91608037421864, 151.23288232673644),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.91851096391805, 151.2344058214569),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.91818154739766, 151.2346203981781),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.91727341958453, 151.23348314155578),
      type: "library",
    },
  ];

  features.forEach((feature) => {
    new google.maps.Marker({
      position: feature.position,
      icon: icons[feature.type].icon,
      map: map,
    });
  });

  const legend = document.getElementById("legend") as HTMLElement;

  for (const key in icons) {
    const type = icons[key];
    const name = type.name;
    const icon = type.icon;
    const div = document.createElement("div");

    div.innerHTML = '<img src="' + icon + '"> ' + name;
    legend.appendChild(div);
  }

  map.controls[google.maps.ControlPosition.RIGHT_BOTTOM].push(legend);
}

declare global {
  interface Window {
    initMap: () => void;
  }
}
window.initMap = initMap;

JavaScript

let map;

function initMap() {
  map = new google.maps.Map(document.getElementById("map"), {
    zoom: 16,
    center: new google.maps.LatLng(-33.91722, 151.23064),
    mapTypeId: "roadmap",
  });

  const iconBase = "https://maps.google.com/mapfiles/kml/shapes/";
  const icons = {
    parking: {
      name: "Parking",
      icon: iconBase + "parking_lot_maps.png",
    },
    library: {
      name: "Library",
      icon: iconBase + "library_maps.png",
    },
    info: {
      name: "Info",
      icon: iconBase + "info-i_maps.png",
    },
  };
  const features = [
    {
      position: new google.maps.LatLng(-33.91721, 151.2263),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91539, 151.2282),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91747, 151.22912),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.9191, 151.22907),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91725, 151.23011),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91872, 151.23089),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91784, 151.23094),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91682, 151.23149),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.9179, 151.23463),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91666, 151.23468),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.916988, 151.23364),
      type: "info",
    },
    {
      position: new google.maps.LatLng(-33.91662347903106, 151.22879464019775),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.916365282092855, 151.22937399734496),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.91665018901448, 151.2282474695587),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.919543720969806, 151.23112279762267),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.91608037421864, 151.23288232673644),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.91851096391805, 151.2344058214569),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.91818154739766, 151.2346203981781),
      type: "parking",
    },
    {
      position: new google.maps.LatLng(-33.91727341958453, 151.23348314155578),
      type: "library",
    },
  ];

  features.forEach((feature) => {
    new google.maps.Marker({
      position: feature.position,
      icon: icons[feature.type].icon,
      map: map,
    });
  });

  const legend = document.getElementById("legend");

  for (const key in icons) {
    const type = icons[key];
    const name = type.name;
    const icon = type.icon;
    const div = document.createElement("div");

    div.innerHTML = '<img src="' + icon + '"> ' + name;
    legend.appendChild(div);
  }

  map.controls[google.maps.ControlPosition.RIGHT_BOTTOM].push(legend);
}

window.initMap = initMap;

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;
}

#legend {
  font-family: Arial, sans-serif;
  background: #fff;
  padding: 10px;
  margin: 10px;
  border: 3px solid #000;
}

#legend h3 {
  margin-top: 0;
}

#legend img {
  vertical-align: middle;
}

HTML

<html>
  <head>
    <title>Custom Legend</title>
    <script src="https://polyfill.io/v3/polyfill.min.js?features=default"></script>

    <link rel="stylesheet" type="text/css" href="./style.css" />
    <script type="module" src="./index.js"></script>
  </head>
  <body>
    <div id="map"></div>
    <div id="legend"><h3>Legend</h3></div>

    <!-- 
     The `defer` attribute causes the callback to execute after the full HTML
     document has been parsed. For non-blocking uses, avoiding race conditions,
     and consistent behavior across browsers, consider loading using Promises
     with https://www.npmjs.com/package/@googlemaps/js-api-loader.
    -->
    <script
      src="https://maps.googleapis.com/maps/api/js?key=AIzaSyB41DRUbKWJHPxaFjMAwdrzWzbVKartNGg&callback=initMap&v=weekly"
      defer
    ></script>
  </body>
</html>

Try Sample

The sections below explain the main steps to create a legend.

Creating the legend container

The table below explains the code that customizes the legend.

Code and description
<div id="legend"><h3>Legend</h3></div>

Creates a div to hold the content.
Adds a heading level three (3) to the div.
map.controls[google.maps.ControlPosition.RIGHT_BOTTOM].push
(document.getElementById('legend'));

Positions the div at the right-bottom of the map by adding a control position.
Read about more control position options.
<style>
  #legend {
    font-family: Arial, sans-serif;
    background: #fff;
    padding: 10px;
    margin: 10px;
    border: 3px solid #000;
  }
</style>

Styles the legend control using CSS.

Adding the legend content

Use the existing marker styles definition to populate the legend.

var legend = document.getElementById('legend');
for (var style in styles) {
  var name = style.name;
  var icon = style.icon;
  var div = document.createElement('div');
  div.innerHTML = '<img src="' + icon + '"> ' + name;
  legend.appendChild(div);
}