People visit roughly 25 places

Interesting study summarized over at The Economist. The researchers tracked the movements of 40,000 people as they went about their daily lives. They found the number of places that people go to regularly is about 25. That set of 25 places changes, but when someone adds a new place they tend to stop going to the old place. The result is kind of like a Dunbar’s number but for places, not relationships.

The article is a good summary but the paper is of course more detailed. Evidence for a conserved quantity in human mobility. If you ask a friendly librarian in Taiwan (speaking Russian when asking) they might give you this download link.

To be honest I didn’t get a lot more out of the paper than the Economist article. The statistical methods are unfamiliar to me and I’m too lazy to figure them out. But some details:

  • They define a “place” as anywhere someone dwells more than 10 minutes. These are characterized as “places offering commercial activities, metro stations, classrooms and other areas within the University campus”
  • People discover new places all the time. The fit is exponential, roughly
    locations = days ^ 0.7 over a span of ~1000 days.
  • The probability a new place becomes part of the permanent set is somewhere between 7% and 20%. The Lifelog dataset (their largest) yields 7%; the others are 15-20%.
  • There’s four separate datasets. Sony Lifelog is the big one; that’s like Google Timeline combined with a fitness tracker. But also several academic datasets. One of those, the Reality Mining Dataset from the MIT Media Lab is publicly available and covers 94 people.

Interesting research. I wonder if it’s really true? It seems plausible enough and matches my personal experience. Particularly since I split time between two cities; I go to fewer places in San Francisco regularly now that I am half time in Grass Valley.