Sized Points on a Map
A world map displays cities with populations over 50,000 as semitransparent circles, sized proportionally to their population using a square-root scale. The visualization uses React for the user interface and D3 v5’s `geoNaturalEarth1` projection with `geoPath` to render country boundaries, graticules, and a sphere backdrop. City data comes from Simplemaps, while country shapes come from World Atlas TopoJSON. Circles are positioned via the projection and sized using `scaleSqrt` from D3, with opacity set through CSS.