The contact network of Mexico City.

Physical contacts are at the core of most human interactions. These contacts form large networks of physical interactions that are guided by social, economic, and urban factors, and through which complex dynamics, from product exchange to disease spread, can occur. The characterization of these contact networks for large settings, such as a metropolitan area, is unfeasible without the use of technological approaches.
In this work, we characterised the contact network for Mexico City, using mobile device position data. For the day of 2020-02-18, we analysed 10 minute time windows to identify the position of devices within a fine-grained (<0.9m2) hexagonal tesselation of the city. For each time window, we represented this positions as a bipartite device-position network, which we projected to identify co-localization events. We joined all these co-localization networks to generate a single network capturing all close contacts of device owners. The resulting network was characterized in terms of its topology. We identified that this network has a heavy-tailed degree distribution, and a well defined modular structure.
We used device position data to infer the residence of each mobile device. We used this information to characterize the spatial and socioeconomic patterns that are captured by the network. The majority of contacts occur between devices that are resident of the same neighborhoods; with intra-neighborhood contacts being more common in less affluent neighborhoods. Nevertheless, contacts between residents of geographically distant neighborhoods are also observed; even contacts with residents of nearby cities. We further characterized whether these contacts are more frequent between residents of geographically distant neighborhoods with similar socioeconomic indicators, identifying specific patterns of connectivity.
This work has been used in the context of the current COVID-19 emergency to advise and orient public policy decision makers with regards of the social dynamics observed within Mexico City.