Notes

Based on a large sample of publicly available Twitter data, our study shows that a substantial share of ties lies within the
same metropolitan region, and that between regional clusters, distance, national borders and language
differences all predict Twitter ties.We find that the frequency of airline flights between the two parties is
the best predictor of Twitter ties. This highlights the importance of looking at pre-existing ties between
places and people.

Conclusion:

Looking at the network of ties in Twitter we find that distance
and related variables (language, country, and the number of flights)
all have an effect on Twitter ties despite the seeming ease with
which long range ties can be formed. Our analysis shows,
however, that distance considerably constrains ties. Two fifths of
ties (39 percent) connect users within the same regional cluster,
typically the size of a metropolitan area. All such ties are domestic
and connect users in the same linguistic area. Most of them fall
within easy driving distance. Even for the remaining longer range
ties between different clusters, distance matters. Ties at distances
of up to 1000 km are more frequent than what we would expect if
the ties were formed randomly, while ties longer than 5000 km are
underrepresented.
For the longer ties, distance, language differences, country
boundaries, and ease of travel can vary independently, even as
they remain strongly correlated. This warrants a comparison of
such variables. We find that country and the frequency of flights
have independent effects in pair-wise comparisons.

The number of airline flights emerges as the best predictor of
non-local Twitter ties. This likely reflects the role of air travel in
facilitating long-distance face-to-face interaction, which in turn
influences the formation of electronic ties. Air travel can also stand
as a proxy for other kinds of pre-existing connections between
places, which in turn influence formation of electronic ties. These
findings highlight the importance of considering structural constraints
on ties rather than simple physical distance.