Self-organized criticality and urban form system dynamics with reference to a Brazilian city.

This study of the evolution of urban forms examines the relationship between urban expansion (the enlargement of an urban area) and densification (the increase in the volume of the built form). Densification involves infinitesimally small, dispersed accretions, while the expansion of the urban surface involves the incorporation of larger areas usually on the edge of a city. As a result, built-form density grows steadily to the precise moment when a new urban land is added, when it suddenly falls, only to grow again until a new catastrophe occurs. This paper provides evidence that the size and duration of urban land accretions exhibit power-law distributions for both size and duration, and that the break points that occur when density falls due to new urban land accretion are predictable. These results provide further evidence that urban systems are characterized by self-organized criticality. [ABSTRACT FROM AUTHOR]