Population, light, and the size distribution of cities

We provide new insights on the city size distribution of countries around the world. Using geo-spatial data and a globally consistent city identification scheme, our data set contains 13,844 cities in 194 countries. City size is measured both in terms of population and night time lights proxying for local economic activity. We find that Zipf's law holds for many, but not all, countries in terms of population, while city size in terms of light is distributed more unequally. These deviations from Zipf's law are to a large extent driven by an undue concentration in the largest cities. They benefit from agglomeration effects which seem to work through scale rather than through density. Examining the cross-country heterogeneity in the city size distribution, our model selection approach suggests that historical factors play an important role, in line with the time of development hypothesis.