This choropleth map of the United States visualizes a sample cost index by state, using a yellow-green-blue sequential color scale to show values ranging roughly from 84 to 160. The visualization loads US state boundaries as TopoJSON from the us-atlas package and renders them with d3.geoPath and an Albers USA projection. Each state’s color is determined by looking up its FIPS code in a cost-index dataset, and hovering reveals a tooltip with the state name and value using plain DOM events and D3 styling.