This interactive map of U.S. Air Quality Index (AQI) data for 2021 uses a d3.geoAlbersUsa projection with d3.geoPath to render state boundaries, while a quantitative color scale encodes AQI values at each monitoring site. A linked d3.brushX histogram below the map shows monthly mean AQI, and brushing a time range filters the map’s bubbles to show only data from that period. The visualization is built with React, uses d3.scaleQuantile for color mapping, and d3.histogram for binning, with data loaded via d3.csv from a GitHub source.