Agents, Cells, and Cities: New Representational Models for Simulating Multiscale Urban Dynamics

New forms of representation at a fine spatial scale, in which units of space are conceived as cells and populations as individual agents, are currently changing the way we are able to simulate the evolution of cities. In this paper I show how these new approaches are consistent with traditional urban models that have gone before, with the emphasis no longer being on spatial interaction but on development dynamics and local movement. I first introduce ideas about urban simulation based on spatial evolution as reaction and diffusion, showing how problems conceived in terms of cells and/or agents enable new implementations of this generic model. I sketch the rudiments of cellular automata which emphasise rules for development transition, and agent-based models which focus on how individuals respond to environmental attributes encoded in cellular landscapes. I illustrate these exemplars through models of residential location. Three applications are then presented at very different spatial scales: pedestrian movement at the building scale, the evolution of systems of cities at a regional scale, and urban growth at the city scale. I conclude with proposals that formal policy analysis in this domain should always be informed by more than one approach.