If you go to the API and extract data from there, tweets, authors, users data and other informations are there. We are analysing this sort of data (500 000 tweets in three months extraction ! following a social movement). Regarding user locations, we found two possibilities:
a). the information that provide the people who write the tweet. I mean: User X says that he/she is in the X place (for instance, Madrid), but it could be imprecise or a lie (we found both case). So problems at analising.
b). the information base on GPS data, more objective, but in our experience, uncompleted, as people sometimes do not allow the mobile to provide this data when you open a twitter account.
So it depend on the importance for you of having user locations complete or not, trusty or not. Good job ahead !
Podargos can help you find data from Twitter by machine learning. All you have to do is to tell them your needs.
It can provide twitter historical and realtime data. In additional, it's able to help you retrieve other mobile App data of social networks and e-commerce, and supports for nearly 100 languages.