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Cities and Regions as Self-Organizing Systems: Models of Complexity
ABSTRACT This book sets out the basic ideas underlying complexity and the qualitative, spatial evolution that it allows. It describes the conceptual framework of modelling, showing the assumptions involved in developing models which are: a) deterministic, non-linear equations, b) self-organizing dynamical systems, c) evolutionary systems. The paper then describes the mathematical modelling of the spatial self-organization that occurs in regional and urban development as a result of the interaction of economic, demographic and environmental factors. There are chapters on interurban evolution and the emergence of urban hierarchies, with several examples described in detail. It then moves on to intra-urban evolution, and again uses several examples to show how the ideas of complexity allow us to look at emergence and structural change in cities as different economic and residential functions generate interdependent patterns of land-use and of transport flows. It is a model of the multiple decision making processes that go on in the system, concerning short term flows of people, goods and services, involved in commuting and in the supply chain of the economic system, and also the longer term processes that drive migration and the spatial pattern of investment. There are at least two levels of description for the system. The first concerns individuals in small zones attempt to pursue their own goals, and those of their job, and a second, more macroscopic scale, of the urban and regional structure that results. This macroscopic structure, however, fashions the costs and benefits that enter into the individual/local decision making processes, giving rise to a "self-organization" of the system, as the micro and macro levels interact. Rather than predicting exact paths of the system the method is more useful in exploring the different kind of alternatives that are possible, and to perform a strategic analysis of different possible qualitative structures which the system might evolve. Several examples of these models will be briefly discussed: the Brussels Model within Belgium, other national models such as Senegal, the changing urban hierarchy of the USA reflecting migration flows, as well as interventions in intra-urban evolution that serve to demonstrate the potential usefulness of such systems.