Visitors to the area around Nature's London offices will be familiar with the scene: unending traffic and noise; the hurly-burly of the Underground; streets, concourses and platforms filled with people intent only on reaching their destination quickly. It's received wisdom that the bigger a city is, the faster life moves; Luis Bettencourt and colleagues supply some empirical evidence to back up that perception (Proc. Natl Acad. Sci. USA 104, 7301–7306; 2007).
The authors begin by examining how different indicators of cities' activity and infrastructure scale with their size. They use various sets of data from the United States, China and Germany, and characterize the scalings as power laws of the form (population)n. They find that indicators of economic activity — from personal income, to patent registrations, to total electricity consumption — vary with population with values of n in the range 1.1–1.3, regardless of where the data were collected. In other words, cities the world over become more hyperactive the larger they get. Perhaps as a corollary to that excess, the prevalence of crime and sexually transmitted disease grows similarly quickly.
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