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World’s Subways Converging on Ideal Form | Wired Science | Wired.com
By Brandon Keirn
May 15, 2012

After decades of urban evolution, the world’s major subway systems appear to be converging on an ideal form … [Statistical physicist Marc] Barthelemy and National Center for Scientific Research complex systems analyst Camille Roth focused a network analysis lens on the aforementioned cities’ subways, along with Barcelona, Beijing, Berlin, Chicago, Madrid, Mexico, Moscow, Osaka, Paris, Seoul and Tokyo … Patterns emerged: The core-and-branch topology, of course, and patterns more fine-grained. Roughly half the stations in any subway will be found on its outer branches rather than the core. The distance from a city’s center to its farthest terminus station is twice the diameter of the subway system’s core. This happens again and again.

“Many other shapes could be expected, such as a regular lattice,” said Barthelemy. “What we find surprising is that all these different cities, on different continents, with different histories and geographical constraints, lead finally to the same structure.”

Subway systems seem to gravitate towards these ratios organically, through a combination of planning, expedience, circumstance and socioeconomic fluctuation, say the researchers … The convergence “is a sign that there are some basic, profound mechanisms that drive the development of urban systems,” said Barthelemy. 

(vía humanscalecities)