Bursts and Avalanches : The Dynamics of Polycentric Urban Evolution

Urban construction activities are subject to periods of fast expansion followed by periods of slow growth. Some of these expansions are limited is size, while other are huge. Therefore, it is not surprising that equilibrium oriented classical models of urban spatial structure are hard pressed to explain the formation of modern cities with polycentric structure and births of sub-centers in particular. To understand the development of cities’ spatial pattern we present a model of urban spatial dynamics that is driven by real estate entrepreneurs of two types that differ in the degree of risk aversion. The developers act in the shadow of city planning board that formulates urban development policy and defines the boundaries of future residential expansions. Its salient feature is the time lag between the time of purchase of property rights by land developers and the time of the realizations of revenues. We assume that this lag varies in space, being much larger in locations that are not zoned for building. It can be reduced by the planning board in cases of high demand for dwellings. With the model we demonstrate how the interaction between demand for dwellings, the choices taken by each type of developers and planning policies lead to the creation of new urban sub-centers. Model dynamics is characterized by long out of equilibrium periods followed by sudden bursts of construction activity that resembles self-organized criticality (SOC)