A proportional symbol map displays the relative housing cost index for each U.S. state, with circle size scaled by the square-root of the housing cost value and the top ten most expensive states highlighted in red. The visualization uses D3 v3 with `d3.geo.path` to render state boundaries from TopoJSON and U.S. state centroids, overlaid with circles sized via `d3.scale.sqrt`. Hovering over a symbol reveals a tooltip with the state name and its housing cost.