This visualization displays the populations of major world cities as scaled circles on a natural Earth projection map. A dropdown menu selects how many top cities to show, while a slider adjusts the maximum circle radius. The map uses D3’s `geoNaturalEarth1` and `geoPath` for rendering landmasses and graticules, with `scaleSqrt` mapping population to circle area. Data comes from the Data Canvas Sense Your City dataset, loaded via `d3.csv` and TopoJSON world atlas features.