This interactive visualization combines a choropleth map of the United States with a linked time-series histogram to explore Air Quality Index (AQI) data by state. The map, rendered with d3.geoPath and geoAlbersUsa, colors each state using a quantile scale based on AQI values. The histogram below aggregates daily readings into monthly bins, and users can brush across it to filter the map’s coloring. Built with React and d3.v5, it loads CSV data from a GitHub gist and US state boundaries from a TopoJSON file.