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/v0.37.0/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.37.0/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 on a feature in the states layer, open a popup at the
    // location of the click, with description HTML from its properties.
    map.on('click', 'states-layer', function (e) {
        new mapboxgl.Popup()
            .setLngLat(e.lngLat)
            .setHTML(e.features[0].properties.name)
            .addTo(map);
    });

    // Change the cursor to a pointer when the mouse is over the states layer.
    map.on('mouseenter', 'states-layer', function () {
        map.getCanvas().style.cursor = 'pointer';
    });

    // Change it back to a pointer when it leaves.
    map.on('mouseleave', 'states-layer', function () {
        map.getCanvas().style.cursor = '';
    });
});
</script>

</body>
</html>
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