Individual mobility and social behaviour: Two sides of the same coin

According to personality psychology, personality traits determine many aspects of human behaviour. However, validating this insight in large groups has been challenging so far, due to the scarcity of multi-channel data. Here, we focus on the relationship between mobility and social behaviour by analysing two high-resolution longitudinal datasets collecting trajectories and mobile phone interactions of ∼ 1000 individuals. We show that there is a connection between the way in which individuals explore new resources and exploit known assets in the social and spatial spheres. We point out that different individuals balance the exploration-exploitation trade-off in different ways and we explain part of the variability in the data by the big five personality traits. We find that, in both realms, extraversion correlates with an individual’s attitude towards exploration and routine diversity, while neuroticism and openness account for the tendency to evolve routine over long time-scales. We find no evidence for the existence of classes of individuals across the spatio-social domains. Our results bridge the fields of human geography, sociology and personality psychology and can help improve current models of mobility and tie formation. Introduction Two forces shape our social and spatial behaviour. On the one hand, we all experience limitations [1]. Time, cognition, age, the need for food, etc. all constrain our behaviour. On the other hand, each one of us is characterised by personality traits that make us, if perhaps not unique, at least different from many. Personality psychology conjectured a long ago that a set of personality traits underlie all aspects of human behaviour [2, 3]. In the social realm, individuals cope with cognitive and temporal constraints by establishing and maintaining connections in a distinctive [4, 5] and persistent [4] manner. For example, the size of an individual’s social circle is bounded under ∼ 150, the so-called Dunbar number [6], but varies among individuals around this limit [7]. These differences result from an interplay between physical and extrinsic factors such as gender [8], age [9] and socio-economic status [10] as well as from stable individual dispositions underlying personality [11]. Spatially, individuals are characterised by an activity space of repeatedly visited locations within which they move during their daily activities [12], but this geo-spatial signature varies in size [13] and spatial shape [14]. However, unlike the social case, the conjecture that individuals’ spatial behaviour is persistent in time [15] had not been verified until recently. Here, we capitalise on the recent discovery that the size of the activity space is conserved and correlates with the social circle size [16] to test the conjecture that the same personality dispositions in part determine social and spatial behaviour. We test this theory by analysing two long-term datasets consisting of ∼ 1000 individuals mobility trajectories and their phone interactions (for previous studies see section ‘State of the art ’ below). First, we test the hypothesis that the strategies individuals adopt in order to choose where to go and with whom to interact are similar. Then, we identify and characterise the prevailing socio-spatial 1 ar X iv :1 80 1. 03 96 2v 1 [ ph ys ic s. so cph ] 1 1 Ja n 20 18 profiles appearing in the datasets. Finally, we show that socio-spatial profiles can be partially explained by the widely adopted big-five personality trait model, often used to describe aspects of the social and emotional life [7,11,17–22]. In the section ‘State of the art ’, we review the relevant literature; in ‘Methods’ we describe data collection and pre-processing, and we provide details of the methods implemented; in ‘Results’ we present our findings. State of the art Individual-level variability in social and spatial behaviour has mostly been investigated in isolation so far, with few notable efforts to reconcile the two. Here, we briefly review the empirical findings in the two domains. The social domain Individuals deal with limited time and cognitive capacity resulting in finite social networks [6, 23] by distributing time unevenly across their social circle [4, 24–28]. While this is a shared strategy, there is clear evidence for individual-level variation. First, social circles vary in terms of diversity: they differ in size [7] within a maximum upper-bound of ∼ 150 individuals [6] and in structure [4, 29]. Second, individuals display different attitudes towards exploration of social opportunities as they are more or less keen on creating new connections [30–33]. Finally, individuals manage social interactions over time in different ways. Some are characterised by high level of stability as they maintain a very stable social circle, while others renew their social ties at high pace [5]. These heterogeneities can be partially explained by factors including gender [8, 34], age [9, 35, 36], socio-economic status [10, 37] and physical attractiveness [38]. Moreover, as conjectured by personality psychologists [2,39], differences in personalities partially explain the variability in social circle composition [7,11,17,40–44], and the different attitudes towards forming [30,45], developing [20,46] and replacing [29] social connections. It is worth noticing that many of these findings are recent, resulting from the analysis of digital communication traces. The spatial domain Constraints including physical capabilities, the distribution of resources, and the need to coordinate with others limit our possibilities to move in space [1]. Individuals cope with these limitations by allocating their time within an activity space of repeatedly visited locations [47], whose size is conserved over several years according to a recent study based on high-resolution trajectories [16], and previous ones based on unevenly sampled and low spatial resolution data [48,49]. The activity space varies across individuals in terms of size [16] and shape [14]: it was shown that two distinct classes of individuals can be identified based on the spatial distribution of their locations, similarly to the social domain [5]. Heterogeneities in spatial behaviour can be explained in terms of gender [50], age [51, 52], socio-economic [35, 53] and ethnic [54] differences. There has only been sporadic efforts to include personality measures in geographic research, despite the strong connections between the two [55]. Recent works [44,56] suggest that spatial behaviour can be partially explained from personality traits. However, in [56], this understanding is based on biased data collected from location-based social networks. In [44], the connection between spatial behaviour and personality is not investigated extensively, as it is not the main focus of the study. Social and spatial connection Recently, connections between the social and spatial behaviour of pairs [57–62] and groups [63] of individuals have been demonstrated, and used to design predictive models of mobility [58, 64, 65] or social ties [59,66–68]. Shifting the attention to the individual level, recent works based on online social network data [69, 70], mobile phone calls data [62] and evenly sampled high resolution mobility trajectories [16] have shown correlations between the activity space size and the ego network structure, calling for further research to more closely examine the connections between social and spatial behaviour at the individual level.