From Morris Davis, Jonas Fisher, and Toni Whited:
Cities exist because of the productivity gains that arise from clustering production and workers, a process called agglomeration. How important is agglomeration for aggregate growth? This paper constructs a dynamic stochastic general equilibrium model of cities and uses it to estimate the effect of lo- cal agglomeration on aggregate growth. We combine aggregate time-series and city-level panel data to estimate the model’s parameters via generalized method of moments. The estimates imply a statistically and economically significant impact of local agglomeration on the growth rate of per capita consumption, raising it by about 10%.