Understanding spatial homophily: the case of peer influence and social selection

Homophily is a phenomenon observed very frequently in social networks and is related with the inclination of people to be involved with others that exhibit similar characteristics. The roots of homophily can be subtle and are mainly traced back to two mechanisms: (i) social selection and (ii) peer influence. Decomposing the effects of each of these mechanisms requires analysis of longitudinal data. This has been a burden to similar studies in traditional social sciences due to the hardness of collecting such information. However, the proliferation of online social media has enabled the collection of massive amounts of information related with human activities. In this work, we are interested in examining the forces of the above mechanisms in the context of the locations visited by people. For our study, we use a longitudinal dataset collected from Gowalla, a location-based social network (LBSN). LBSNs, unlike other online social media, bond users' online interactions with their activities in real-world, physical locations. Prior work on LBSNs has focused on the influence of geographical constraints on the formation of social ties. On the contrary, in this paper, we perform a microscopic study of the peer influence and social selection mechanisms in LBSNs. Our analysis indicates that while the similarity of friends' spatial trails at a geographically global scale cannot be attributed to peer influence, the latter can explain up to 40% of the geographically localized similarity between friends. Moreover, this percentage depends on the type of locations we examine, and it can be even higher for specific categories (e.g., nightlife spots). Finally, we find that the social selection mechanism, is only triggered by places that exhibit specific network characteristics. We believe that our work can have significant implications on obtaining a deeper understanding of the way that people create friendships, act and move in real space, which can further facilitate and enhance applications such as recommender systems, trip planning and marketing.