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Measure distances

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Click points on a map to create lines that measure distanced using turf.length.

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Measure distances</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no">
<link href="https://api.mapbox.com/mapbox-gl-js/v3.8.0/mapbox-gl.css" rel="stylesheet">
<script src="https://api.mapbox.com/mapbox-gl-js/v3.8.0/mapbox-gl.js"></script>
<style>
body { margin: 0; padding: 0; }
#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<style>
    .distance-container {
        position: absolute;
        top: 10px;
        left: 10px;
        z-index: 1;
    }

    .distance-container > * {
        background-color: rgba(0, 0, 0, 0.5);
        color: #fff;
        font-size: 11px;
        line-height: 18px;
        display: block;
        margin: 0;
        padding: 5px 10px;
        border-radius: 3px;
    }
</style>

<div id="map"></div>
<div id="distance" class="distance-container"></div>

<script src="https://unpkg.com/@turf/turf@6/turf.min.js"></script>
<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',
        // Choose from Mapbox's core styles, or make your own style with Mapbox Studio
        style: 'mapbox://styles/mapbox/streets-v12',
        center: [2.3399, 48.8555],
        zoom: 12
    });

    const distanceContainer = document.getElementById('distance');

    // GeoJSON object to hold our measurement features
    const geojson = {
        'type': 'FeatureCollection',
        'features': []
    };

    // Used to draw a line between points
    const linestring = {
        'type': 'Feature',
        'geometry': {
            'type': 'LineString',
            'coordinates': []
        }
    };

    map.on('load', () => {
        map.addSource('geojson', {
            'type': 'geojson',
            'data': geojson
        });

        // Add styles to the map
        map.addLayer({
            id: 'measure-points',
            type: 'circle',
            source: 'geojson',
            paint: {
                'circle-radius': 5,
                'circle-color': '#000'
            },
            filter: ['in', '$type', 'Point']
        });
        map.addLayer({
            id: 'measure-lines',
            type: 'line',
            source: 'geojson',
            layout: {
                'line-cap': 'round',
                'line-join': 'round'
            },
            paint: {
                'line-color': '#000',
                'line-width': 2.5
            },
            filter: ['in', '$type', 'LineString']
        });

        map.on('click', (e) => {
            const features = map.queryRenderedFeatures(e.point, {
                layers: ['measure-points']
            });

            // Remove the linestring from the group
            // so we can redraw it based on the points collection.
            if (geojson.features.length > 1) geojson.features.pop();

            // Clear the distance container to populate it with a new value.
            distanceContainer.innerHTML = '';

            // If a feature was clicked, remove it from the map.
            if (features.length) {
                const id = features[0].properties.id;
                geojson.features = geojson.features.filter(
                    (point) => point.properties.id !== id
                );
            } else {
                const point = {
                    'type': 'Feature',
                    'geometry': {
                        'type': 'Point',
                        'coordinates': [e.lngLat.lng, e.lngLat.lat]
                    },
                    'properties': {
                        'id': String(new Date().getTime())
                    }
                };

                geojson.features.push(point);
            }

            if (geojson.features.length > 1) {
                linestring.geometry.coordinates = geojson.features.map(
                    (point) => point.geometry.coordinates
                );

                geojson.features.push(linestring);

                // Populate the distanceContainer with total distance
                const value = document.createElement('pre');
                const distance = turf.length(linestring);
                value.textContent = `Total distance: ${distance.toLocaleString()}km`;
                distanceContainer.appendChild(value);
            }

            map.getSource('geojson').setData(geojson);
        });
    });

    map.on('mousemove', (e) => {
        const features = map.queryRenderedFeatures(e.point, {
            layers: ['measure-points']
        });
        // Change the cursor to a pointer when hovering over a point on the map.
        // Otherwise cursor is a crosshair.
        map.getCanvas().style.cursor = features.length
            ? 'pointer'
            : 'crosshair';
    });
</script>

</body>
</html>
This code snippet will not work as expected until you replace YOUR_MAPBOX_ACCESS_TOKEN with an access token from your Mapbox account.
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