Urban interactions and spatial structure

This article specifies and solves a model of endogenous spatial interactions where agents choose to visit a particular location to interact with others. Equilibrium fails to achieve first-best levels of visits and population density. A construction subsidy can restore second-best efficiency, but not first-best because it does not operate on the visit margin directly. A transportation subsidy can achieve first best. This result-which contrasts with earlier work-comes from treating interaction as a choice variable, rather than focusing on population density, a correlate. Developers are unable to implement even second-best efficiency because of their limited control over a city's land area.