This example displays a world map with cities plotted as semi-transparent circles, where circle size reflects each city’s population. It uses a natural Earth projection via `d3.geoNaturalEarth1` and `d3.geoPath` to render land, graticules, and country borders from TopoJSON data. City coordinates and populations come from a CSV loaded with `d3.csv`, and circle radii are scaled with `d3.scaleSqrt`. The visualization is built with React hooks for data fetching and renders as SVG.