Cities, scales, and complexity

Brown bag seminar 

Date: Monday, January 19, 2015; 12:30 – 13:30

Place: Techno-Z, GI-lecture room: SC30EG0.E07 (Schillerstraße 30, building 15, ground floor)

Presenter: Dr. Mark Padgham (Institute for Geoinformatics, University of Münster)

The study of complex systems has been strongly dominated by examinations of "scale-free" or power-law patterns and processes, reflecting its origins in Per Bak's (1987-88) simple models of collapsing sand piles, in which the sizes of avalanches are power-law distributed. The fact that power-law distributions have no meaningful central moments presents, however, a fundamental difficulty in preventing reference to mean states or properties. Reports of power-law adherence also dominate recent urban science, as reflected most notably in Luis Bettencourt's prominent Science article (2014) in which he reveals the wealth of properties of urban systems that manifest power-law distributions, including city size, population density, infrastructure, crime, health, and transport. Cities nevertheless have defined scales. Houses are built to scales typical of the morphology of Homo sapiens. The structure of lanes, streets, and roads reflect typical gaits of humans and our beasts and vehicles of conveyance, and the scale of city blocks reflects in turn the scales of the ways that bound them. Urban science to date generallly treats such entities as "atomic", and pursues examinations of the scaling behaviour of aggregated houses, streets, and city blocks. In these cases, scaling behaviour emerges from the aggregation of such atomic units. There is nevertheless one other fundamentally important "unit" of all urban spaces that is not atomic, and that only emerges following initial aggregation: the neighbourhood. Neighbourhoods are in effect imposed a posteriori onto aggregations of "atomic units," and very commonly manifest their own intrinsic scales. I will present results of my research into urban scales, and use that to illustrate how cities offer unique systems in which to attempt what has not yet been formally achieved for complex systems in any general sense, namely the reconciliation of fixed-scale processes and properties within a general scale-free dynamic.