Show polygon information on click
When a user clicks a polygon, show a popup containing more information.
<!DOCTYPE html>
<html>
<head>
    <meta charset='utf-8' />
    <title></title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.34.0/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.34.0/mapbox-gl.css' rel='stylesheet' />
    <style>
        body { margin:0; padding:0; }
        #map { position:absolute; top:0; bottom:0; width:100%; }
    </style>
</head>
<body>

<style>
.mapboxgl-popup {
    max-width: 400px;
    font: 12px/20px 'Helvetica Neue', Arial, Helvetica, sans-serif;
}
</style>
<div id='map'></div>
<script>
mapboxgl.accessToken = '<your access token here>';
var map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/mapbox/streets-v9',
    center: [-100.04, 38.907],
    zoom: 3
});

map.on('load', function () {

    // Add a layer showing the state polygons.
    map.addLayer({
        'id': 'states-layer',
        'type': 'fill',
        'source': {
            'type': 'geojson',
            'data': 'https://d2ad6b4ur7yvpq.cloudfront.net/naturalearth-3.3.0/ne_110m_admin_1_states_provinces_shp.geojson'
        },
        'paint': {
            'fill-color': 'rgba(200, 100, 240, 0.4)',
            'fill-outline-color': 'rgba(200, 100, 240, 1)'
        }
    });
});


// When a click event occurs near a polygon, open a popup at the location of
// the feature, with description HTML from its properties.
map.on('click', function (e) {
    var features = map.queryRenderedFeatures(e.point, { layers: ['states-layer'] });
    if (!features.length) {
        return;
    }

    var feature = features[0];

    var popup = new mapboxgl.Popup()
        .setLngLat(map.unproject(e.point))
        .setHTML(feature.properties.name)
        .addTo(map);
});

// Use the same approach as above to indicate that the symbols are clickable
// by changing the cursor style to 'pointer'.
map.on('mousemove', function (e) {
    var features = map.queryRenderedFeatures(e.point, { layers: ['states-layer'] });
    map.getCanvas().style.cursor = (features.length) ? 'pointer' : '';
});
</script>

</body>
</html>
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