Sometimes it feels like there just aren’t enough hours in the day to see everybody and do everything. Now we can put a figure on the number of places you’re likely to go to, and it’s way fewer than you’d think.
While we all have different habits that change over time, a recent study looked at how people move about in their everyday lives. It turns out the mathematics governing the number of places we visit on a frequent basis surprisingly doesn’t change all that much – and you spend the majority of your life spread out around 25 places.
Mathematicians from the University of London wanted to know if human mobility evolved as lifestyles changed, or if it was relatively stable over time.
To solve the question, they used data on the movements of Danish university students that had been collected as a part of a previous study on social interactions.
The Copenhagen Network Study already had a bank of GPS locations and wifi scans tracking the lives of 851 volunteers, providing a detailed map of where individuals went over an extended period.
The two researchers crunched the figures to categorise their daily movements.
“We first analysed the traces of about 1,000 university students,” says researcher Laura Alessandretti.
The numbers showed that over a 24 month period, the students mostly kept to just a handful of locations, defined as an activity space.
Interestingly, while the precise make-up of this activity space varied over time as priorities changed and new locations were discovered, its overall size didn’t shift.
“I expected to see a difference in the behaviour of students and a wide section of the population,” says Alessandretti. “But that was not the case.”
To characterise the activity space’s structure, the researchers created categories depending on how long they spent in any one spot.
Some, such as at home, were measured in dozens of hours per week. Others, such as bus stops, added up to just few minutes.
While the activity space’s structure depends on how you define things like location, once you’ve set limits on those it seems we all follow the same pattern.
For the purposes of these studies, a familiar location is any you return to at least twice in a given week for 10 minutes or more at a time.
The formula implies that our total capacity for these locations is a sum of the time we allocate to our general movements.
This makes sense. If a change in our usual schedule gives us an hour to spare, we tend to replace what we did before with a different hour-long activity we’d recently found an interest in.
“People are constantly balancing their curiosity and laziness,” says senior author Andrea Baronchelli.
“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.”
But Danish students are one thing. To test their model, the pair took their method to the next level and incorporated another three data sets.
“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,” says Alessandretti.
“It was not expected in advance. It came as a surprise.”
Whether you’re a middle-aged bus driver in Paris or a young teacher in Sydney, we max out at around 25 locations in our activity set. Even if the places themselves change.
Before you think this is simply because we can’t squeeze more into a busy schedule, one of the studies tested the real data against randomly shuffled data to test that idea. This showed that time constraints would still allow us the capacity to visit more than 25 places. So it seems that there must be another reason.
“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.
This figure is reminiscent of another figure that imposes a limit on our lives – Dunbar’s number.
Anthropologist Robin Dunbar once determined we can only really maintain a connection with about 150 people in our social network, and of those we only have five really good friends.
There will always be exceptions to these rules, but for the most part it seems that our social brains are still constrained by resources that mean we don’t stretch ourselves when it comes to keeping important people and places in mind.
This research was published in Nature.