Open Data are increasingly seen as a new and very relevant resource, that can dramatically change the landscape of the services and infrastructure in urban environments. This opportunity is often conceptualized by defining open data as a new common. Open data however, are not necessarily a commons, at least in the sense defined by Bollier [1], they are rather a shareable resource, which will only be accessed and used if a community exists around them and a set of practices and rules are defined to manage them. This paper is focusing on those two aspects: the creation of a community of users and a set of practices that regulate and facilitate the use of open data. Communities and practices, the two elements that would turn open data into a common, are not emerging spontaneously; their emergence needs to be appropriately designed.