A choropleth map of the United States colors each state according to its cost-of-living index from a CSV of expensive states, with tooltips revealing additional cost rank details on hover. The visualization uses D3 v7 and TopoJSON to load and render state boundaries via `d3.geoPath` with an Albers USA projection. A sequential blue color scale maps cost index values, while an interactive tooltip div appears on mouseover to show state-specific data.