This choropleth map shows Massachusetts town boundaries colored by county, with an interactive legend that highlights matching regions on hover. The visualization uses React with d3.v5, including `d3.geoAlbers` for projection and `d3.geoPath` for rendering SVG paths from TopoJSON data. A CSV file maps towns to counties, and the legend employs `d3.scaleOrdinal` with a custom `ColorLegend` component. Hovering a legend value dims non-matching towns via reduced opacity while brightening the selected county.