  In this paper, a model (called the elliptic model) is proposed to estimate
the number of social ties between two locations using population data in a
similar manner to how transportation research deals with trips. To overcome the
asymmetry of transportation models, the new model considers that the number of
relationships between two locations is inversely proportional to the population
in the ellipse whose foci are in these two locations. The elliptic model is
evaluated by considering the anonymous communications patterns of 25 million
users from three different countries, where a location has been assigned to
each user based on their most used phone tower or billing zip code. With this
information, spatial social networks are built at three levels of resolution:
tower, city and region for each of the three countries. The elliptic model
achieves a similar performance when predicting communication fluxes as
transportation models do when predicting trips. This shows that human
relationships are influenced at least as much by geography as is human
mobility.
