A world map displays population changes by country from 2020 to 2030 using animated, scaled circles. D3's `geoNaturalEarth1` projection and `geoPath` render the landmasses, while `transition().delay()` sequentially animates each country circle's radius to reflect yearly population estimates from a CSV file. A legend using `scaleSqrt` and `sizeLegend` explains the circle-size mapping, and hovering highlights individual countries.