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Measure distances

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

const map = new maplibregl.Map({
    container: 'map',
    style: 'https://tiles.openfreemap.org/styles/bright',
    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';
});

<!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 property="og:created" content="2025-06-25" />
    <meta charset='utf-8'>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel='stylesheet' href='https://unpkg.com/maplibre-gl@5.24.0/dist/maplibre-gl.css' />
    <script src='https://unpkg.com/maplibre-gl@5.24.0/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://cdn.jsdelivr.net/npm/@turf/turf@7/turf.min.js"></script>
<script>
    const map = new maplibregl.Map({
        container: 'map',
        style: 'https://tiles.openfreemap.org/styles/bright',
        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>