  The idea of a hierarchical spatial organization of society lies at the core
of seminal theories in human geography that have strongly influenced our
understanding of social organization. In the same line, the recent availability
of large-scale human mobility and communication data has offered novel
quantitative insights hinting at a strong geographical confinement of human
interactions within neighboring regions, extending to local levels within
countries. However, models of human interaction largely ignore this effect.
Here, we analyze several country-wide networks of telephone calls and uncover a
systematic decrease of communication induced by borders which we identify as
the missing variable in state-of-the-art models. Using this empirical evidence,
we propose an alternative modeling framework that naturally stylize the damping
effect of borders. We show that this new notion substantially improves the
predictive power of widely used interaction models, thus increasing our ability
to predict social activities and to plan the development of infrastructures
across multiple scales.
