Product differentiation,monopolistic competition and city size

Traditionally, the formation of cities has been explained by such supply-side phenomena as scale economies in production or such demand-side phenomena as public goods. This paper presents an integrated demand and supply approach to the formation of cities in spatial economy. Demand considerations, in the form of consumer agglomeration economies (i.e., product variety), are presented as a major cause of urban agglomeration. On the supply side, scale economies are introduced. Both aspects are examined by using the Dixit-Stiglitz model of monopolistic competition to characterize the equilibrium and optimum city size. We also discuss a subsidy scheme that produces an equilibrium city size corresponding to a first-best optimum. Then we analyze the distribution of population in a system of two cities.