This chapter focuses on understanding the interactions using location-based social media as a way to reflect on the technological support of human activities. It presents a summary of findings emerging from human-centred computing research on Foursquare, and integrates the results from studies of Foursquare use that have conducted in two cities. Digital interactions are increasingly interwoven with spaces and places in urban settings, with such interactions mediated by and in turn shaping the technologies that facilitate them. The perspective is that of human-centred computing, particularly Computer-Supported Cooperative Work a multidisciplinary field studying collaborative practices in socio-technical systems, with a focus on unearthing and detailing the mediational role of technology in human cooperation, coordination and social interaction. The chapter discusses the issues concerning LBSN, both drawing from and consolidating the findings of human-centred computing literature on physical or digital interactions using location-based social media, and from empirical studies of LBSN use that have conducted in two cities.