This visualization shows a proportional symbols map of U.S. states, where circle size encodes each state’s cost index and the top nine highest-cost states appear in red. It uses D3 v7 with SVG rendering, a `d3.geoAlbersUsa` projection, and `d3.geoPath` for both state boundaries and symbol placement. A `d3.scaleSqrt` maps cost indices to circle radii. The code loads state polygons from us-states.json and point data from expensive-states.json, adding tooltips on mouse events.