This interactive choropleth map visualizes 2024 Boston Marathon finisher data across U.S. states, with a clickable legend to toggle between four metrics: number of finishers, average finish time, average age, and average second-half split difference. The map uses D3’s `geoAlbers` projection and `geoPath` to render state boundaries from TopoJSON via `topojson-client`, while CSV data is parsed with `csvParse`. Hover effects and a tooltip are implemented with D3 selections, and color scales from `scaleLinear` update state fills dynamically.