This example displays a map of US counties using GeoJSON data, rendered as SVG paths with a steelblue fill. It uses D3’s `geoAlbersUsa` projection and `geoPath` to convert geographic coordinates into screen paths, with the map fitted to the container’s dimensions. Hovering over a county increases its opacity from 0.5 to 1 via a CSS class toggle, creating a subtle interactive highlight. The data comes from Plotly’s `geojson-counties-fips` dataset, loaded asynchronously with D3’s `json` method.