A choropleth map of the United States visualizes a diversity index for each state, ranging from white to blue via a linear color scale. The visualization uses D3 v4 with `d3.geoAlbersUsa` for projection and `d3.geoPath` to render state boundaries from TopoJSON data. State polygons are filled based on a hardcoded dataset of diversity values, and hovering highlights the state with a thicker stroke. The code includes a commented-out tooltip and a legend using `d3.legendColor`, though neither is fully implemented.