If you feel like there’s not enough time in the day to do everything you want and see everyone you’d want to see, then you’re probably right.

We wake up, go to work (or school), go to the shop, back home, maybe we eat at our favorite place, have a cup of coffee, maybe visit a few friends but how many places do we really go to (more than a couple of times)? Mathematicians from the University of London wanted to know the answer to that question, so they set out to map human mobility, and they found that at any given period in our lives, we hang around about 25 places.

Behind the project are Dr. Laura Alessandretti and Dr. Andrea Baronchelli, who work in London, and Professor Sune Lehmann from DTU Technical University of Denmark and the research team from Sony Mobile Communications. They analyzed university students — a group believed to visit more places and be more active than the population average. But results were surprising: over the 24 months of the study, students mostly kept to just a handful of locations.

“We first analysed the traces of about 1,000 university students. The dataset showed that the students returned to a limited number of places, even though the places changed over time. I expected to see a difference in the behavior of students and a wide section of the population. But that was not the case. The result was the same when we scaled up the project to 40,000 people of different habits and gender from all over the world. It was not expected in advance. It came as a surprise,” says Dr. Alessandretti.

This could teach us a lot about our very nature. We are, through our nature, curious creatures, but we also don’t like too much hassle — in a way, we also conserve our mental (and physical) energy.

“People are constantly balancing their curiosity and laziness. We want to explore new places but also want to exploit old ones that we like. Think of a restaurant or a gym. In doing so we adopt and abandon places all the time. We found that this dynamic yields an unexpected result: We visit a constant, fixed number of places—and it’s not due to lack of time. We found evidence that this may be connected to other limits to our life, such as the number of active social interactions we can maintain in our life, but more research is in order to clarify this point,” says Dr. Baronchelli

When they further expanded their data set to 40,000 people, the results were invariably the same: whether you’re a student in Copenhagen, a bus driver in Paris, or an engineer in New York, you can’t really go above 25 active locations at one time, even though the locations themselves might change.

“Our research established a first formal connection between the study of human mobility and human social cognition. Clarifying this link will help us design better public spaces as well as better transportation systems. And ultimately facilitate the creation of more sustainable and healthy urban environment for all of us,” Dr. Baronchelli adds.

Interestingly, this is yet another factor that limits our social habits, in addition to Dunbar’s number. An anthropologist and evolutionary psychologist, Dunbar’s name is strongly associated with a single number: 150. The theory of Dunbar’s Number posits that 150 is the number of individuals with whom any one person can maintain stable relationships with, and out of these, only five or so are considered to be good friends.

“We found evidence that this may be connected to other limits to our life, such as the number of active social interactions we can maintain in our life, but more research is in order to clarify this point,” says Baronchelli.

Journal Reference: Laura Alessandretti et al. Evidence for a conserved quantity in human mobility, Nature Human Behaviour (2018). DOI: 10.1038/s41562-018-0364-x

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