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Measure distances

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

<!DOCTYPE html>
<html lang="en">
<head>
    <title>Measure distances</title>
    <meta property="og:description" content="Click points on a map to create lines that measure distanced using turf.length." />
    <meta charset='utf-8'>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel='stylesheet' href='https://unpkg.com/maplibre-gl@4.4.0/dist/maplibre-gl.css' />
    <script src='https://unpkg.com/maplibre-gl@4.4.0/dist/maplibre-gl.js'></script>
    <style>
        body { margin: 0; padding: 0; }
        html, body, #map { height: 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://npmcdn.com/@turf/turf@5.1.6/turf.min.js"></script>
<script>
    const map = new maplibregl.Map({
        container: 'map',
        style:
            'https://api.maptiler.com/maps/streets/style.json?key=get_your_own_OpIi9ZULNHzrESv6T2vL',
        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) => {
                    return 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) => {
                        return point.geometry.coordinates;
                    }
                );

                geojson.features.push(linestring);

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

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

    map.on('mousemove', (e) => {
        const features = map.queryRenderedFeatures(e.point, {
            layers: ['measure-points']
        });
        // UI indicator for clicking/hovering a point on the map
        map.getCanvas().style.cursor = features.length ?
            'pointer' :
            'crosshair';
    });
</script>
</body>
</html>