This example displays a choropleth map of the United States, with each county filled in green and outlined in brown, and hovering turns a county yellow. It uses the D3.js library's `geoPath` and `geoAlbersUsa` projection to render the map, drawing from the `us-atlas` counties-10m GeoJSON data source. County data is loaded via a JSON request, and the map’s SVG elements are built dynamically using D3’s selection and data-binding methods.