## 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.
<iframe src="https://geo-devrel-javascript-samples.web.app/samples/inset-map/app/dist/" allow="fullscreen; "></iframe>

### TypeScript

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

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

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

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

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

> [!NOTE]
> **Note:** Read the [guide](https://developers.google.com/maps/documentation/javascript/using-typescript.md.txt) on using TypeScript and Google Maps.

### JavaScript

```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,
      ),
    );
  });
}

window.initMap = initMap;
```

> [!NOTE]
> **Note:** The JavaScript is compiled from the TypeScript snippet.

### CSS

```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

```html
<html>
  <head>
    <title>Inset Overview Map</title>

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

    <!-- 
      The `defer` attribute causes the script 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. See
      https://developers.google.com/maps/documentation/javascript/load-maps-js-api
      for more information.
      -->
    <script
      src="https://maps.googleapis.com/maps/api/js?key=AIzaSyB41DRUbKWJHPxaFjMAwdrzWzbVKartNGg&callback=initMap&v=weekly"
      defer
    ></script>
  </body>
</html>
```

### Clone Sample


Git and Node.js are required to run this sample locally. Follow these [instructions](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm) to install Node.js and NPM. The following commands clone, install dependencies and start the sample application.

```javascript
  git clone -b sample-inset-map https://github.com/googlemaps/js-samples.git
  cd js-samples
  npm i
  npm start
```


Other samples can be tried by switching to any branch beginning with `sample-SAMPLE_NAME`.

```javascript
  git checkout sample-SAMPLE_NAME
  npm i
  npm start
```