Cities

City questions almost always hinge on a boundary. A city proper, a metropolitan area and a built-up urban zone can differ by a factor of five for the same place, and which one a statistic uses changes the answer more than any measurement uncertainty does. Read the question carefully before estimating.

The reliable method is to work from population and density rather than from impressions. A city of a given size needs a predictable number of restaurants, schools, metro stations and bridges, because those scale with people rather than with fame. Estimating infrastructure from population is far more accurate than estimating it from how big a city feels.

The other theme here is constraint. Cities take their shape from what they physically cannot do — a mountain, a coastline, a protected greenbelt, a drained lakebed — far more than from what they choose. Several of the most surprising figures in this category are consequences of geography rather than of planning or wealth.