Circles on a Map
This visualization displays the global population infected by COVID-19, using proportional circles placed at country centroids on a natural Earth projection. The map shows both countries with and without reported data, colored differently, while a size legend and color legend explain the scaling. The implementation uses d3's geoPath, geoNaturalEarth1, and geoCentroid for map projections, and scaleSqrt for circle sizing, with data loaded from a CSV and TopoJSON atlas.