A `Dunbar's number' in human mobility

Tuesday, February 27, 2018

2:30 p.m.

ISI seminar room 1st floor

Laura Alessandretti City, University of London

Recent seminal works on human mobility have shown that individuals constantly exploit a small set of repeatedly visited locations. A       concurrent literature has emphasised the explorative nature of human behaviour, showing that the number of visited places grows steadily over time. How to reconcile these seemingly contradicting  facts remains an open question. In this talk, we present an analysis of high-resolution multi-year traces of ~40,000  individuals from 4 datasets and we 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 ~25 locations. We use this finding to improve state-of-the-art       modelling of human mobility. Furthermore, shifting the attention from aggregated quantities to individual behaviour 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's number' describing a cognitive upper limit to an individual's number of social relations.