Automata-based exploration of emergent urban form

The impact of technological change on urban form has been inordinately difficult to model using traditional approaches to urban theory. Most modeling strategies assume urban structure to be in some form of equilibrium or at best, assume some dynamic whose equilibrium properties are well-defined. Discontinuous change such as the development of new communications technologies and the development of new modes of retailing and work are rarely considered; most modeling efforts assume the existence of these technologies and simply develop their spatial consequences. However in the last decade, systems theorists have begun to articulate new principles for handling discontinuities and bifurcations, the relationship between local and global change, and the role of positive feedback in simulating surprising and novel departures from existing trends. In this paper, we review the state of the art, arguing that these principles are best reflected in a style of urban modeling which depends on the framework of cellular automata (CA). We propose a framework to handle urban evolution which encompasses a set of generic tools capable of: capturing the processes of evolutionary urban dynamics at the finest level through the concepts of growth generators and growth locators; handling interactions between local action and environmental and regional socio-economic trends through a constraint input alphabet; delineating positive feedbacks among neighborhoods, districts, and regions; and linking the overall imagability of the city with local change as articulated through transition rules. We illustrate these ideas through a series of experiments which simulate a variety of urban forms. We also show how multiple centers can be simulated and how decentralized and diffuse urban form results from simulating development based on the spontaneous evolution of route-street systems. © 1997 OPA (Overseas Publishers Association) Amsterdam B.V. Published in The Netherlands under license by Gordon and Breach Science Publishers.