This example visualizes concentric geo-circles radiating from two fixed points on a world map: the North Pole and Washington, D.C. It uses `d3.geoCircle()` to generate spherical circles at increasing radii, with `d3.geoPath()` and an equirectangular projection to render them as SVG paths. The code draws the circles in red and blue before overlaying landmasses from TopoJSON. It demonstrates how d3.v4’s geographic circle generator computes geodesic rings, with radii ranging from 5 to 85 degrees. The map is rendered at 960×500 pixels using D3’s `d3.geoEquirectangular` projection.