The Evolution of the City Size Distributions

We review the accumulated knowledge on city size distributions and determinants of urban growth. This topic is of interest because of a number of key stylized facts, including notably Zipf’s law for cities (which states that the number of cities of size greater than S is propor-tional to 1/S) and the importance of urban primacy. We first review the empirical evidence on the upper tail of city size distribution. We offer a novel discussion of the important econometric issues in the char-acterization of the distribution. We then discuss the theories that have been advanced to explain the approximate constancy of the distribu-tion across very different economic and social systems, emphasizing both bare-bone statistical theories and more developed economic the-ories. We discuss the more recent work on the determinants of urban growth and, in particular, growth regressions, economic explanations of city size distributions other than Gibrat’s law, consequences of ma-jor shocks (quasi natural experiments), and the dynamics of U.S. urban evolution