This proportional-symbol map visualizes the cost index for each U.S. state, with circle size encoding the index value and the top 10 states highlighted in black. The visualization uses D3.js v7 with a Mercator projection via `d3.geoPath()` and `d3.geoMercator()`, rendering state boundaries as SVG paths. State coordinates and cost index data are loaded from CSV files, while geographic boundaries come from a GeoJSON source. Circles positioned at state centroids use radius values scaled from the cost index, with tooltips showing exact values.