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Highlight features containing similar data

In this example, a user can hover their cursor over any United States county in the map view. The map highlights other U.S. counties with a matching name in the visible viewport and displays a popup with information about the highlighted features.

The example uses mousemove to get the first county feature that the mouse is moving over. Then it uses querySourceFeatures to create a list of county features from source tiles in the visible viewport that match the name of the current county. Since querySourceFeatures can return duplicate features when they cover multiple tiles, it implements a custom function to remove duplicates.

To create the highlighted polygon effect, it uses setFilter to display only the matching counties on the counties-highlighted layer.

Use a custom tileset

This example uses U.S. county data uploaded to Mapbox as a vector tileset. This data is not updated or maintained and should not be used in production applications. If you're interested in creating an application that uses U.S. county data, you can download a Shapefile from's data portal and upload it to Mapbox Studio's Tilesets page.

<!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">
<link href="" rel="stylesheet">
<script src=""></script>
body { margin: 0; padding: 0; }
#map { position: absolute; top: 0; bottom: 0; width: 100%; }
.map-overlay {
12px/20px 'Helvetica Neue',
background-color: #fff;
box-shadow: 0 1px 2px rgba(0, 0, 0, 0.1);
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_MAPBOX_ACCESS_TOKEN';
const map = new mapboxgl.Map({
container: 'map',
// Choose from Mapbox's core styles, or make your own style with Mapbox Studio
style: 'mapbox://styles/mapbox/streets-v12',
center: [-98, 38.88],
minZoom: 2,
zoom: 3

const overlay = document.getElementById('map-overlay');

// Create a popup, but don't add it to the map yet.
const popup = new mapboxgl.Popup({
closeButton: false

// Because features come from tiled vector data,
// feature geometries may be split
// or duplicated across tile boundaries.
// As a result, features may appear
// multiple times in query results.
function getUniqueFeatures(features, comparatorProperty) {
const uniqueIds = new Set();
const uniqueFeatures = [];
for (const feature of features) {
const id =[comparatorProperty];
if (!uniqueIds.has(id)) {
return uniqueFeatures;

map.on('load', () => {
// Add a custom vector tileset source. The tileset used in
// this example contains a feature for every county in the U.S.
// Each county contains four properties. For example:
// {
// COUNTY: "Uintah County",
// FIPS: 49047,
// median-income: 62363,
// population: 34576
// }
map.addSource('counties', {
'type': 'vector',
'url': 'mapbox://mapbox.82pkq93d'
// Add transparent county polygons
// for default display.
'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 polygons under labels, roads and buildings.

// Add filled county polygons
// for highlighted display.
'id': 'counties-highlighted',
'type': 'fill',
'source': 'counties',
'source-layer': 'original',
'paint': {
'fill-outline-color': '#484896',
'fill-color': '#6e599f',
'fill-opacity': 0.75
// Display none by adding a
// filter with an empty string.
'filter': ['in', 'COUNTY', '']
// Place polygons under labels, roads and buildings.

map.on('mousemove', 'counties', (e) => {
// Change the cursor style as a UI indicator.
map.getCanvas().style.cursor = 'pointer';

// Use the first found feature.
const feature = e.features[0];

// Query the counties layer visible in the map.
// Only onscreen features are returned.
// Use filter to collect only results
// with the same county name.
const relatedCounties = map.querySourceFeatures('counties', {
sourceLayer: 'original',
filter: ['in', 'COUNTY',]

// Remove duplicates by checking for matching FIPS county ID.
const uniqueCounties = getUniqueFeatures(relatedCounties, 'FIPS');

// Total the populations of all features.
const populationSum = uniqueCounties.reduce((memo, feature) => {
return memo +;
}, 0);

// Render found features in an overlay.
const title = document.createElement('strong');
title.textContent = +
' (' +
uniqueCounties.length +
' found)';

const population = document.createElement('div');
population.textContent =
'Total population: ' + populationSum.toLocaleString();

overlay.innerHTML = ''; = 'block';


// Add features with the same county name
// to the highlighted layer.
map.setFilter('counties-highlighted', [

// Display a popup with the name of the county.

map.on('mouseleave', 'counties', () => {
map.getCanvas().style.cursor = '';
map.setFilter('counties-highlighted', ['in', 'COUNTY', '']); = 'none';

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