Evidence for a Conserved Quantity in Human Mobility

TL;DR

This study uncovers a conserved set of approximately 25 locations in individual human mobility patterns, reconciling previous conflicting observations about exploration and exploitation behaviors over long-term periods.

Contribution

It reveals a conserved mobility quantity in humans and links it to social interaction limits, advancing understanding of human movement and social behavior.

Findings

Mobility patterns evolve smoothly over time.

Individuals typically visit around 25 familiar locations.

The conserved mobility set correlates with social interaction limits.

Abstract

Recent seminal works on human mobility have shown that individuals constantly exploit a small set of repeatedly visited locations. A concurrent literature has emphasized the explorative nature of human behavior, showing that the number of visited places grows steadily over time. How to reconcile these seemingly contradicting facts remains an open question. Here, we analyze high-resolution multi-year traces of $\sim$40,000 individuals from 4 datasets and show that this tension vanishes when the long-term evolution of mobility patterns is considered. We reveal that mobility patterns evolve significantly yet smoothly, and that the number of familiar locations an individual visits at any point is a conserved quantity with a typical size of $\sim$25 locations. We use this finding to improve state-of-the-art modeling of human mobility. Furthermore, shifting the attention from aggregated quantities to individual behavior, we show that the size of an individual's set of preferred locations correlates with the number of her social interactions. This result suggests a connection between the conserved quantity we identify, which as we show can not be understood purely on the basis of time constraints, and the `Dunbar number' describing a cognitive upper limit to an individual's number of social relations. We anticipate that our work will spark further research linking the study of Human Mobility and the Cognitive and Behavioral Sciences.