A choropleth map of EPA air quality recording sites displays colored circles over US state boundaries, with each circle sized by AQI values. The visualization uses d3.geoAlbersUsa and d3.geoPath for map rendering and d3.scaleQuantile for color encoding. A date histogram below uses d3.histogram to bin daily AQI readings by month, with brushX filtering the map to show only data within a selected time range. Both components are built with React and render SVG elements.