Abstract

Christopher Alexander, a British-American scholar, differentiated an old (natural) city from a new (planned) one by structure. The former resembles a “semilattice”, or a complex system encompassing many interconnected sub-systems. The latter is shaped in a graph-theoretical “tree”, which lacks the structural complexity as its sub-systems are compartmentalized into a single hierarchy. This structural distinction explains why, or perhaps determines “the patina of life” in old urban districts and the lack of such in new ones. His idea, although widely influential, remains contested for its lack of empirical evidence. Subsequent literature failed to distinguish the structural differences between the old and new cities in systematic ways, nor is his hypothesized structure-life relationship verified with statistical rigor. This study aims to test Alexander’s urban structural theory under a comprehensive research framework. We translated his constructs and premises into a mathematically testable form. Qualities of urban spatial structure, such as “semilattice”, “complex network” and “living structure”, were measured using graph-topological indicators computed for street networks. Urban life was measured using a combination of Twitter activities, Point-Of-Interests, and walking trips at the district level. The structure-life relationship was examined using statistical models, after controlling for urban form and socio-demographic confounders including land use, density, block size, parks, income, age, and demographic groups. This research design was implemented in London, New York, Hong Kong, and Gdansk. Our results support Alexander's early works that an old urban district contains more “semilattice” compared with new ones. This quality can be consistently captured by Meshedness Coefficient, a graph-network indicator for semilattice-shaped street network and a strong predictor for urban life. The same cannot be observed for “complex network” with consistency, while we found no independent associations between “living structure” and life, contrary to existing literature. The study shed light on the hidden relationship between urban spatial structure and behavioral evidence in both the virtual and physical world. We uncovered the British-American predilection of Alexander’s theory, which matched data closely in London and New York, but less so in Hong Kong and Gdansk, suggesting the need for a locally-sensitive approach.

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Authors (6)