A map of the United States displays the country's boundary as a GeoJSON layer over an OpenStreetMap tile base. The example loads state boundaries from `us-states.geojson` and renders them using Leaflet’s `L.geoJSON` and `L.tileLayer` APIs. It demonstrates integrating Leaflet with a plain HTML page, centering the view on the nation at zoom level four, and fetching geographic data asynchronously. The code includes D3 imports and local ES6 modules but uses only Leaflet for the actual mapping.