The new paper, authored by statistical physicist Marc Barthelemy of France's National Center for Scientific Research, and appearing in the Journal of the Royal Society Interface, compared the layout of subway systems around the world (including New York City, Tokyo, London, Barcelona, Beijing, and many others) using a network analysis lens to look for underlying trends.
According to Keim, 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."
"Subway systems seem to gravitate towards these ratios organically, through a combination of planning, expedience, circumstance and socioeconomic fluctuation, say the researchers," which, promisingly, "may hint at universal principles of human self-organization."