This example uses a natural Earth projection to render a world map with circles sized by 2018 population estimates. The visualization displays countries in two colors, distinguishing those with population data from those without. It uses d3.geoNaturalEarth1, d3.geoPath, and d3.geoCentroid to project country boundaries and position circles at country centroids. A d3.scaleSqrt maps population values to circle radii, with a custom size legend and zoom interaction via d3.zoom. Population data comes from a CSV file merged with TopoJSON world atlas geometry.