A choropleth map of the United States colors each state by its average Air Quality Index (AQI) using a quantile color scale. Below the map, a brushable time-series histogram displays monthly AQI means, enabling users to filter the map’s data by date range. Built with React and D3 v5, it uses `geoAlbersUsa` and `geoPath` for the map projection and `scaleQuantile` for color encoding, with data loaded from a CSV. The brush applies a `brushX` interaction to adjust the histogram’s visible domain.