This choropleth map of U.S. counties assigns a distinct categorical color to each state using `d3.scaleOrdinal` with `d3.schemeCategory10`. The map projects geographic data with `d3.geoPath` and a `d3.geoAlbersUsa` projection, rendering counties as SVG paths with red strokes and a blue hover effect. It loads TopoJSON county boundaries from the `us-atlas` package and includes a tooltip with each county’s state name via appended `title` elements. The visualization uses `d3.v5` and the `topojson` library for feature extraction.