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The MIT Senseable City Lab recently teamed up with a few other research groups to investigate the relationship between human interactions and city size. If you happen to be a member of the Journal of the Royal Society Interface, you can download the full report here. But in true ATC fashion, I’m going to give you the Coles Notes version here.

What the study did was look at billions of anonymized mobile phone data in both Portugal and the UK in order to determine how our real life social networks change with city size. And what they found is a pretty consistent relationship:

[T]his study reveals a fundamental pattern: our social connections scale with city size. The larger the town you live in, the more people you call and the more calls you make. The scaling of this relation is “super-linear,” which means that on average, if you double the size of a town, the sum of phone contacts in the city will more than double – in a mathematically predictable way.

What’s interesting about this finding is that it starts to explain how cities—and the clustering of people—can act as fertile ground for the exchange of ideas and knowledge. The bigger the city the more people you probably know.

But what I’m curious about (I don’t have the report) is if there’s some kind of upper limit. Presumably this “super-linear” relationship tapers off after a certain city size, because there has got to be limits to the number of people we can maintain productive relationships with.

According to British anthropologist Robin Dunbar, that number was 150 people.