This example shows a world map with graticules and country boundaries, overlaid with small circles representing cities with populations over 50,000. The map uses the `geoNaturalEarth1` projection and `d3.geoPath` to render land, sphere, and graticule paths from TopoJSON data. City positions are projected from latitude and longitude coordinates, and each city is drawn as an SVG circle with opacity. The visualization is built with React and D3 v5, loading data from a CSV of world cities and the World Atlas TopoJSON.