Circles on a Map
This visualization displays global population data for 2018 using proportional circles positioned at country centroids on a natural Earth projection map, with circle area scaled by population via d3.scaleSqrt. Countries lacking data appear in pink, while those with data are gray, and hovering shows a tooltip with the region name and population. Users can pan and zoom the map using d3.zoom, and a size legend generated with d3.ticks communicates the population scale. The visualization relies on d3.geoPath and d3.geoCentroid for geographic rendering, TopoJSON for world boundaries, and CSV data joined by country code to populate each feature.