> For the complete documentation index, see [llms.txt](https://docs.mapbox.com/mapbox-gl-js/llms.txt)
# 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`](https://docs.mapbox.com/mapbox-gl-js/api/map/#map.event:mousemove) to get the first county feature that the mouse is moving over. Then it uses [`querySourceFeatures`](https://docs.mapbox.com/mapbox-gl-js/api/map/#map#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`](https://docs.mapbox.com/mapbox-gl-js/api/map/#map#setfilter) to display only the matching counties on the `counties-highlighted` layer.
> **Note: 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 [census.gov's data portal](https://www.census.gov/geographies/mapping-files/time-series/geo/cartographic-boundary.html) and upload it to Mapbox Studio's [Tilesets page](https://console.mapbox.com/studio/tilesets/).
> Example code:
**JavaScript**
```html
Highlight features containing similar data
```