This map plots U.S. Environmental Protection Agency air quality monitoring sites, with each circle’s radius scaled by the square root of the AQI value. Built with React and D3 v5, it renders a U.S. Albers projection via `d3.geoAlbersUsa` and `d3.geoPath` over a TopoJSON atlas. Animated legend transitions in `colorLegend.js` use D3’s transition API to reflect color scale changes. Data is loaded from a CSV via `d3.csv`, and a D3 zoom interaction lets users inspect regions.