This example divides US states into four color-coded census regions—Northeast, Midwest, South, and West—drawn as fixed geographic projections. It uses D3 v5 with `d3.json`, `d3.geoPath`, and the `topojson` library to merge state geometries from the us-10m.v1 TopoJSON dataset. Each region is rendered as a separate SVG path with distinct fill colors defined in CSS.