By city proper when possible, according to citypopulation.de. Wikipedia, WorldAtlas, and GeoNames are backup sources
Some countries don't have cities, just municipalities. In those cases, we go by the municipality population.
When no reliable source has a sufficient number of cities listed, any city listed by the source will work
Because of lack of good data, Costa Rica, Fiji, and South Africa are by urban area
By city proper when possible, according to citypopulation.de. Wikipedia, WorldAtlas, and GeoNames are backup sources
Some countries don't have cities, just municipalities. In those cases, we go by the municipality population.
When no reliable source has a sufficient number of cities listed, any city listed by the source will work
Because of lack of good data, Costa Rica, Fiji, and South Africa are by urban area