This example visualizes global population estimates for 2018 using circles overlaid on a natural Earth projection map. Countries with missing data appear pink, while populated areas are gray with semi-transparent cyan circles sized by population via d3.scaleSqrt. The visualization includes an interactive size legend with formatted tick values and a color legend. It uses d3.geoPath, d3.geoCentroid, d3.zoom, and d3.scaleOrdinal, rendering with SVG. Population data comes from a UN CSV file joined to TopoJSON world geometry, with tooltips showing country names and population counts.