This D3.js and React visualization displays a map of US Environmental Protection Agency (EPA) air quality monitoring sites, with each site represented by a circle sized according to its AQI value using a square root scale from `d3.scaleSqrt`. The map is rendered using an SVG-based equirectangular projection via `d3.geoPath` and `geoAlbersUsa`, with US state boundaries and interiors drawn from a TopoJSON atlas loaded through `topojson.feature` and `topojson.mesh`. The underlying data is fetched as a CSV file containing latitude, longitude, and AQI measurements.