Inset Overview Map

Maintaining a geographical frame of reference

An inset map is a smaller map to help the user maintain a geographical frame of reference. The overview map is synchronized with the bounds_changed event on the main map.

JavaScript

const OVERVIEW_DIFFERENCE = 5;
const OVERVIEW_MIN_ZOOM = 3;
const OVERVIEW_MAX_ZOOM = 10;

function initMap() {
  const mapOptions = {
    center: { lat: 50, lng: 8 },
    zoom: 7
  };

  // instantiate the primary map
  map = new google.maps.Map(document.getElementById("map"), {
    ...mapOptions
  });

  // instantiate the overview map without controls
  overview = new google.maps.Map(document.getElementById("overview"), {
    ...mapOptions,
    disableDefaultUI: true,
    gestureHandling: "none",
    zoomControl: false
  });

  function clamp(num, min, max) {
    return Math.min(Math.max(num, min), max);
  }

  map.addListener("bounds_changed", () => {
    overview.setCenter(map.getCenter());
    overview.setZoom(
      clamp(
        map.getZoom() - OVERVIEW_DIFFERENCE,
        OVERVIEW_MIN_ZOOM,
        OVERVIEW_MAX_ZOOM
      )
    );
  });
}

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;
}

#container,
#map {
  height: 100%;
  width: 100%;
}

#map {
  position: relative;
}

#overview {
  position: absolute;
  left: 40px;
  height: 175px;
  width: 175px;
  bottom: 50px;
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.3);
}

HTML

<!DOCTYPE html>
<html>
  <head>
    <title>Inset Overview Map</title>
    <script src="https://polyfill.io/v3/polyfill.min.js?features=default"></script>
    <script
      src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap&libraries=&v=weekly"
      defer
    ></script>
    <link rel="stylesheet" type="text/css" href="./style.css" />
    <script src="./app.js"></script>
  </head>
  <body>
    <div id="container">
      <div id="map"></div>
      <div id="overview"></div>
    </div>
  </body>
</html>

All

<!DOCTYPE html>
<html>
  <head>
    <title>Inset Overview Map</title>
    <script src="https://polyfill.io/v3/polyfill.min.js?features=default"></script>
    <script
      src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap&libraries=&v=weekly"
      defer
    ></script>
    <style type="text/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;
      }

      #container,
      #map {
        height: 100%;
        width: 100%;
      }

      #map {
        position: relative;
      }

      #overview {
        position: absolute;
        left: 40px;
        height: 175px;
        width: 175px;
        bottom: 50px;
        box-shadow: 0 2px 6px rgba(0, 0, 0, 0.3);
      }
    </style>
    <script>
      (function(exports) {
        "use strict";

        let map, overview;
        const OVERVIEW_DIFFERENCE = 5;
        const OVERVIEW_MIN_ZOOM = 3;
        const OVERVIEW_MAX_ZOOM = 10;

        function initMap() {
          const mapOptions = {
            center: {
              lat: 50,
              lng: 8
            },
            zoom: 7
          }; // instantiate the primary map

          map = new google.maps.Map(document.getElementById("map"), {
            ...mapOptions
          }); // instantiate the overview map without controls

          overview = new google.maps.Map(document.getElementById("overview"), {
            ...mapOptions,
            disableDefaultUI: true,
            gestureHandling: "none",
            zoomControl: false
          });

          function clamp(num, min, max) {
            return Math.min(Math.max(num, min), max);
          }

          map.addListener("bounds_changed", () => {
            overview.setCenter(map.getCenter());
            overview.setZoom(
              clamp(
                map.getZoom() - OVERVIEW_DIFFERENCE,
                OVERVIEW_MIN_ZOOM,
                OVERVIEW_MAX_ZOOM
              )
            );
          });
        }

        exports.initMap = initMap;
      })((this.window = this.window || {}));
    </script>
  </head>
  <body>
    <div id="container">
      <div id="map"></div>
      <div id="overview"></div>
    </div>
  </body>
</html>

/* 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; } #container, #map { height: 100%; width: 100%; } #map { position: relative; } #overview { position: absolute; left: 40px; height: 175px; width: 175px; bottom: 50px; box-shadow: 0 2px 6px rgba(0, 0, 0, 0.3); }

<!DOCTYPE html> <html> <head> <title>Inset Overview Map</title> <script src="https://polyfill.io/v3/polyfill.min.js?features=default"></script> <script src="https://maps.googleapis.com/maps/api/js?key=&callback=initMap&libraries=&v=weekly" defer ></script>  </head> <body> <div id="container"> <div id="map"></div> <div id="overview"></div> </div> </body> </html>