An extensible, modular architecture for simulating urban development, transportation, and environmental impacts

UrbanSim simulates the development of urban areas, including land use, transportation, and environmental impacts, over periods of twenty or more years. Its purpose is to aid urban planners, residents, and elected officials in evaluating the long-term results of alternate plans, particularly as they relate to such issues as housing, business and economic development, sprawl, open space, traffic congestion, and resource consumption. From a software perspective, it is a large, complex, system, with heavy demands for excellent space efficiency and support for software evolution. It consists of a collection of models that represent different urban actors and processes, an object store that holds the state of the simulated urban environment, a model coordinator that schedules models to run and notifies them when data of interest has changed, and a translation and aggregation layer that performs a range of data conversions to mediate between the object store and the models. The paper concludes with a discussion of the lessons learned regarding software architecture to support rapid evolution within the field of urban simulation.