This interactive choropleth map displays the percentage of adults age 25 and older with a bachelor's degree or higher across US counties, using data from the USDA Economic Research Service and TopoJSON map data from the US Census Bureau. County polygons are colored on a yellow-green sequential scale via `d3.scaleSequential` and `interpolateYlGn`, with `d3.geoPath` handling the SVG rendering. Hovering over a county reveals a tooltip showing the county name, state, and exact percentage. The visualization also includes a gradient legend built with D3 scales and React components for the header and tooltip.