This example visualizes global population data from the United Nations, using colored circles on a natural Earth projection map. D3’s `geoPath` and `geoCentroid` position each circle over its country’s centroid, while `scaleSqrt` encodes population magnitude through circle radius. A custom `sizeLegend` displays graduated population values, and `colorLegend` provides a color key. The map supports pan and zoom via `d3.zoom`, and country hover effects are styled in CSS. Data is loaded from CSV and TopoJSON, rendered as SVG.