Population agglomeration is a manifest and global trend and appears to be a ubiquitous phenomenon across the world. Thus, it is natural to view economic geography in terms of the system of (economic) cities. There is significant evidence indicating strong correlations between socioeconomic quantities and population sizes of cities, therefore it is of particular interest to know and explain where and what sizes of cities form, and which cities grow or decline. In the September issue of the RIETI Report, we present the column "Constant churning and persistent regularity in population and industrial locations: Evidence from Japan" by Faculty Fellow Tomoya Mori.
Population sizes of cities are highly indicative of their industrial structure. Mori finds that the number of agglomeration cities differ widely across industries, and the industries that are located in a smaller number of cities are found in larger cities, leading to a hierarchical relation in the industrial composition between larger and smaller cities. Another interesting fact is the considerable churning of population and industrial activities among cities in Japan, where the large variation in the population growth of cities clearly reflects the development of highway and high-speed railway networks. Finally, Mori discusses these facts in introducing policy implication, namely, uniform improvement of transport access does not have a monotonic impact on the growth of individual cities and regions, as there are limitations for growth. Such constraints have been mostly neglected and needs to be taken into account in both theoretical and empirical analyses.