Circles on a Map
This visualization displays global population by country using scaled circles positioned at each country’s geographic centroid. Circle area corresponds to population magnitude, with a square-root scale controlling radius. The map supports pan and zoom, and hovering over a country reveals its name and population. Built with D3 v5, it uses `d3.geoNaturalEarth1` for projection, `d3.geoPath` for rendering country outlines from TopoJSON, and `d3.zoom` for interaction. Population data is loaded from a CSV file, and a custom size legend displays tick values using `d3.scaleSqrt`.