This visualization maps Air Quality Index (AQI) data by US county, coloring each county based on its PM2.5 concentration using a quantile color scale from green to red. The map uses `d3.geoAlbers` with `d3.geoPath` to render county boundaries, with counties lacking data shown in grey. The data is loaded from a CSV file and rendered as an SVG within a React application, utilizing the D3.js library.