This paper attempts to analyze both reasons for and consequences of migration under zero population growth using a system of simultaneous differential equations. Assuming that intercity migration is based upon differences in utilities. It is revealed that a deterministic specification of the utility leads to an unstable distribution of city sizes whereas stochastic specifications (the origin-constrained gravity model and the logit mode) do not. It is then argued that population concentration can be explained by an increase in urbanization economies while population decentralization can be due to a decrease in intercity transportation and communication costs.
