We present a study of people’s use of positional information as part of a collaborative location-based game. The game exploits self-reported positioning in which mobile players manually reveal their positions to remote players by manipulating electronic maps. Analysis of players’ movements, position reports and communications, drawing on video data, system logs and player feedback, highlights some of the ways in which humans generate, communicate and interpret position reports. It appears that remote participants are largely untroubled by the relatively high positional error associated with self reports. Our analysis suggests that this may because mobile players declare themselves to be in plausible locations such as at common landmarks, ahead of themselves on their current trajectory (stating their intent) or behind themselves (confirming previously visited locations). These observations raise new requirements for the future development of automated positioning systems and also su...