Mapbox GL JS
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Draw a polygon and calculate its area

This examples allows you to draw a polygon on a map and calculate the area contained in the polygon.

  1. Click the map to begin drawing a polygon.
  2. Double-click when you draw the final vertex to complete the polygon. The total area of the polygon will appear in the lower left corner of the map.
  3. To delete your polygon and draw a new one, use the draw tools on the upper right corner of the map.

The example uses mapbox-gl-draw to draw the polygon and Turf.js to calculate its area in square meters.

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Draw a polygon and calculate its area</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no">
<link href="https://api.mapbox.com/mapbox-gl-js/v2.8.2/mapbox-gl.css" rel="stylesheet">
<script src="https://api.mapbox.com/mapbox-gl-js/v2.8.2/mapbox-gl.js"></script>
<style>
body { margin: 0; padding: 0; }
#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<style>
.calculation-box {
height: 75px;
width: 150px;
position: absolute;
bottom: 40px;
left: 10px;
background-color: rgba(255, 255, 255, 0.9);
padding: 15px;
text-align: center;
}
 
p {
font-family: 'Open Sans';
margin: 0;
font-size: 13px;
}
</style>
 
<script src="https://unpkg.com/@turf/turf@6/turf.min.js"></script>
<script src="https://api.mapbox.com/mapbox-gl-js/plugins/mapbox-gl-draw/v1.2.2/mapbox-gl-draw.js"></script>
<link rel="stylesheet" href="https://api.mapbox.com/mapbox-gl-js/plugins/mapbox-gl-draw/v1.2.2/mapbox-gl-draw.css" type="text/css">
<div id="map"></div>
<div class="calculation-box">
<p>Click the map to draw a polygon.</p>
<div id="calculated-area"></div>
</div>
 
<script>
	// TO MAKE THE MAP APPEAR YOU MUST
	// ADD YOUR ACCESS TOKEN FROM
	// https://account.mapbox.com
	mapboxgl.accessToken = 'YOUR_MAPBOX_ACCESS_TOKEN';
const map = new mapboxgl.Map({
container: 'map', // container ID
style: 'mapbox://styles/mapbox/satellite-v9', // style URL
center: [-91.874, 42.76], // starting position [lng, lat]
zoom: 12 // starting zoom
});
 
const draw = new MapboxDraw({
displayControlsDefault: false,
// Select which mapbox-gl-draw control buttons to add to the map.
controls: {
polygon: true,
trash: true
},
// Set mapbox-gl-draw to draw by default.
// The user does not have to click the polygon control button first.
defaultMode: 'draw_polygon'
});
map.addControl(draw);
 
map.on('draw.create', updateArea);
map.on('draw.delete', updateArea);
map.on('draw.update', updateArea);
 
function updateArea(e) {
const data = draw.getAll();
const answer = document.getElementById('calculated-area');
if (data.features.length > 0) {
const area = turf.area(data);
// Restrict the area to 2 decimal points.
const rounded_area = Math.round(area * 100) / 100;
answer.innerHTML = `<p><strong>${rounded_area}</strong></p><p>square meters</p>`;
} else {
answer.innerHTML = '';
if (e.type !== 'draw.delete')
alert('Click the map to draw a polygon.');
}
}
</script>
 
</body>
</html>