This choropleth map displays world population data for select countries, using a blue sequential color scale to encode each nation's population in millions. The visualization is built with D3.v7 and topojson-client, loading geographic boundaries from a world-atlas dataset and using a Natural Earth projection via `d3.geoNaturalEarth1`. Hovering over a country triggers a tooltip showing its name and population, with `d3.scaleSequential` and `d3.interpolateBlues` driving the color mapping.