This example displays cities with populations over 50,000 as sized points on a world map, using a square-root scale to encode population by circle radius. The map renders with the `geoNaturalEarth1` projection and `geoPath` in React, showing graticules and country boundaries from World Atlas TopoJSON. City data comes from Simplemaps via CSV, loaded with `d3.csv`. Circles are drawn with SVG, styled with a teal fill and 0.3 opacity.