The capitals quiz compares metro-area populations — not the city-proper line on the map, but the contiguous urban region that depends on the capital for jobs and infrastructure. Tokyo's 37 million people make Greater Tokyo the largest metro on Earth; Vatican City's few hundred residents make it the smallest.

Surprising contrasts

Cairo has more people than the entire country of Greece. Lima holds nearly a third of Peru's entire population. Jakarta is sinking literally faster than any other major capital. Brasília, purpose-built in the 1960s, is far smaller than the country's commercial center, São Paulo. Brunei's capital, Bandar Seri Begawan, has roughly the same population as a mid-sized American suburb.