What is the best way to conceptualize a city, asks Emily Badger. "Bettencourt, in a paper published today in the journal Science, finally offers up an answer that borrows a bit from physics, economics, sociology, biology and a handful of other disparate reaches of science. We can never get the analogy quite right, he says, because cities are a thing that is found nowhere else in nature."
"At their most fundamental, cities are not really agglomerations of people; they’re agglomerations of connections between people," explains Bettencourt, a physicist with the Santa Fe Institute, in his paper. "All of their other properties – the roads we build to reach each other, the density required to do that, the economic products and ideas we create together – derive from this fact."
"Cities, Bettencourt has concluded, are a 'special kind of social reactor.' And, as such, they all evolve according to a small set of basic principles that can be used to predict the average social, spatial and infrastructure properties of any metropolitan place," says Badger. "Bettencourt’s theoretical framework suggests that a kind of optimal city exists when we have the most social interaction – and social and economic output coming from it – with the least cost of connecting people and goods and ideas to each other."
"The idea that cities are governed by some universal rules of math may make it sound like the urban planner has little control. But, in fact, Bettencourt sees the planner’s job to try to steer cities toward that optimal point (G*) on the above graph. Beyond that point, the number of social interactions in a city can still grow, but the cost of them rises faster than the benefit."