This choropleth shows the percentage of adults aged 25 and older with a bachelor's degree or higher across U.S. counties. The map uses color categories to represent educational attainment levels, with a legend dividing data into four ranges from 0-11% to 35% and above. It is built with D3 v5, converting TopoJSON county boundaries to GeoJSON via `topojson.feature` and rendering them as SVG paths using `d3.geoPath`. The underlying data comes from a USDA Economic Research Service dataset.