Highlight features containing similar data

Hover over counties to highlight counties that share the same name.

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<!DOCTYPE html>
<meta charset='utf-8' />
<title>Highlight features containing similar data</title>
<meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
<script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.53.0/mapbox-gl.js'></script>
<link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.53.0/mapbox-gl.css' rel='stylesheet' />
body { margin:0; padding:0; }
#map { position:absolute; top:0; bottom:0; width:100%; }
.map-overlay {
font: 12px/20px 'Helvetica Neue', Arial, Helvetica, sans-serif;
background-color: #fff;
box-shadow: 0 1px 2px rgba(0,0,0,0.10);
border-radius: 3px;
position: absolute;
width: 25%;
top: 10px;
left: 10px;
padding: 10px;
display: none;
<div id='map'></div>
<div id='map-overlay' class='map-overlay'></div>
mapboxgl.accessToken = '<your access token here>';
var map = new mapboxgl.Map({
container: 'map',
style: 'mapbox://styles/mapbox/streets-v9',
center: [-98, 38.88],
minZoom: 2,
zoom: 3
var overlay = document.getElementById('map-overlay');
// Create a popup, but don't add it to the map yet.
var popup = new mapboxgl.Popup({
closeButton: false
map.on('load', function() {
// Add the source to query. In this example we're using
// county polygons uploaded as vector tiles
map.addSource('counties', {
"type": "vector",
"url": "mapbox://mapbox.82pkq93d"
"id": "counties",
"type": "fill",
"source": "counties",
"source-layer": "original",
"paint": {
"fill-outline-color": "rgba(0,0,0,0.1)",
"fill-color": "rgba(0,0,0,0.1)"
}, 'place-city-sm'); // Place polygon under these labels.
"id": "counties-highlighted",
"type": "fill",
"source": "counties",
"source-layer": "original",
"paint": {
"fill-outline-color": "#484896",
"fill-color": "#6e599f",
"fill-opacity": 0.75
"filter": ["in", "COUNTY", ""]
}, 'place-city-sm'); // Place polygon under these labels.
map.on('mousemove', 'counties', function(e) {
// Change the cursor style as a UI indicator.
map.getCanvas().style.cursor = 'pointer';
// Single out the first found feature.
var feature = e.features[0];
// Query the counties layer visible in the map. Use the filter
// param to only collect results that share the same county name.
var relatedFeatures = map.querySourceFeatures('counties', {
sourceLayer: 'original',
filter: ['in', 'COUNTY', feature.properties.COUNTY]
// Render found features in an overlay.
overlay.innerHTML = '';
// Total the population of all features
var populationSum = relatedFeatures.reduce(function(memo, feature) {
return memo + feature.properties.population;
}, 0);
var title = document.createElement('strong');
title.textContent = feature.properties.COUNTY + ' (' + relatedFeatures.length + ' found)';
var population = document.createElement('div');
population.textContent = 'Total population: ' + populationSum.toLocaleString();
overlay.style.display = 'block';
// Add features that share the same county name to the highlighted layer.
map.setFilter('counties-highlighted', ['in', 'COUNTY', feature.properties.COUNTY]);
// Display a popup with the name of the county
map.on('mouseleave', 'counties', function() {
map.getCanvas().style.cursor = '';
map.setFilter('counties-highlighted', ['in', 'COUNTY', '']);
overlay.style.display = 'none';