This visualization combines a choropleth map of average AQI values by U.S. state with a linked time-series histogram. The map uses d3.geoPath and d3.geoAlbersUsa to render state boundaries, with colors assigned via d3.scaleQuantile. A brush on the histogram filters the map to show only data within a selected date range. The histogram bins daily AQI readings by month using d3.histogram and displays the mean value per bin. React manages the state and rendering, with data loaded from a CSV file.