A world map shades each country according to its latest reported population, using a yellow-orange-red sequential color scale; countries without data appear gray. Hovering reveals a tooltip with the country name and its population. The visualization loads a world TopoJSON atlas and a population CSV, then projects the GeoJSON features with `d3.geoNaturalEarth1` and draws them as SVG paths via `d3.geoPath`. A linear gradient legend with axis ticks shows the population range.