Twitter is one of the most used applications in the current Internet with
more than 200M accounts created so far. As other large-scale systems Twitter
can obtain enefit by exploiting the Locality effect existing among its users.
In this paper we perform the first comprehensive study of the Locality effect
of Twitter. For this purpose we have collected the geographical location of
around 1M Twitter users and 16M of their followers. Our results demonstrate
that language and cultural characteristics determine the level of Locality
expected for different countries. Those countries with a different language
than English such as Brazil typically show a high intra-country Locality
whereas those others where English is official or co-official language suffer
from an external Locality effect. This is, their users have a larger number of
followers in US than within their same country. This is produced by two
reasons: first, US is the dominant country in Twitter counting with around half
of the users, and second, these countries share a common language and cultural
characteristics with US