This map visualization uses a fixed projection to display the four major U.S. census regions—Northeast, Midwest, South, and West—as distinct colored areas. It renders US state boundaries from the `us-10m` TopoJSON dataset, merging state geometries by regional ID using the `topojson` `merge` function. The D3 `select` and `geoPath` APIs generate SVG paths for each region, with styles defined in a stylesheet assigning each region a unique fill color.