Social media users hardly know who is reading their posts, but they form ideas about their readership. Researchers have coined the term imagined audience for the social groups that actors imagine seeing their public communication. However, social groups are not the only aspect that requires imagination: In the potentially borderless online environment, the geographical scope and locations of one’s audience are also unknown. Furthermore, research has demonstrated that imagined audiences vary between people and situations, but what explains these variations is unclear. In this article, we address these two gaps—the geographical scope and predictors of imagined audiences—using data from a mobile experience sampling method study of 105 active Twitter users from Berlin, Germany. Our results show that respondents mostly think of a geographically broad audience, which is spread out across the country or even globally. The imagined geographical scope and social groups depend on both the communicator and the usage situation. While the audience’s social composition especially depends on tweet content and respondents’ sociodemographic characteristics, the geographical scope is best explained by respondents’ biography and personal mobility, including their experience of living in other countries and local residential duration
