Online services provide a range of opportunities for understanding human behaviour through the large aggregate data sets that their operation collects. Yet the data sets they collect do not unproblematically model or mirror the world events. In this paper we use data from Foursquare, a popular location check-in service, to argue for the importance of analysing social media as a communicative rather than representational system. Drawing on logs of all Foursquare check-ins over eight weeks we highlight four features of Foursquare's use: the relationship between attendance and check-ins, event check-ins, commercial incentives to check-in, and lastly humorous check-ins These points show how large data analysis is affected by the end user uses to which social networks are put.