A choropleth map of the United States colors each state by its average Air Quality Index (AQI) value, using a quantile color scale ranging from green to red. A linked time-series histogram below displays monthly mean AQI values, with a brushable interface that filters the map’s state colors based on the selected date range. The visualization uses React and D3 v5, with `d3.geoAlbersUsa` and `d3.geoPath` for map rendering and `d3.brushX` for interactive filtering. Data comes from a CSV of ozone samples collected nationwide.