Fifty Years of Urban Modelling : Macro Statics to Micro Dynamics , in

This chapter presents both a chronological and conceptual history of urban land use-transportation models movement in the context of current developments. Such models –‘urban models’ for short – first appeared in the 1950s in North America and were made possible by two interrelated forces: the development of digital computing from which large-scale simulation emanated, and policy imperatives for testing the effects of large-scale public investments on cities. Essentially, urban models are still pragmatically motivated tools for testing the impact of changes in the locations of land use and transportation on dense and usually large urban agglomerations. Planning and policy determine their rationale although their foundations are built on theoretical ideas which go back to the roots of modern social science and the influence of physics and mathematics from the time of the Enlightenment. During the brief but turbulent years since this field has developed, there have been substantial shifts in viewpoint. Indeed even the paradigms that condition what attributes of the city are to be modeled, and the way such modeling takes place, have changed. We will chart these changes, beginning with a set of intersecting time lines focusing on theo retical origins and practical applications. We will show how urban models were first conceived in aggregative, static terms when the concern was for simulating the way cities appeared at a cross-section in time. This aggregative, static conception of urban structure has slowly given way to one where much more detailed disaggregate activities appear more important and where dynamics rather than statics is the focus. This reflects as much our abilities t o s imulate m ore e laborate c omputational s tructures a nd c ollect better data as any grand theoretical revision of the way we look at the city, although such a revision is now under way As such, this chapter sets a con text for many of the current advances in urban modeling reported elsewhere in this book. 1 Historical Antecedents Wassily Leontieff is best known as the Russian economist who invented the inputoutput model of the economy in the 1920s before he emigrated to the United States where he subsequently spent his life develop ing the idea. In c ontemporary parlance, an input-output model can best be viewed as a large spreadsheet whose