I take the view of a city as a platform. As a platform, a city has infrastructure, processes, organizations, individuals, and technology as components. Additionally, cities are comprised of technical (e.g. sensors), social (e.g. humans), and socio-technical components (e.g. processes). The glue that holds these components together and enables integration and coordination to occur is data and information. The effective and efficient management of information is not only critical to ensure that each of the components operate optimally but also ensures that the overall system, the city, achieves its overall objectives. In this paper, I focus on three key data dimensions in the context of urban informatics: big, open, and mobile data. Key issues within each data dimension are presented. The paper builds on several research projects on smart cities, urban informatics, and policy informatics. Data collected during these projects includes over 45 case studies, over 60 interviews with key informants, analysis of over several thousand pages secondary data, and an examination of over 70 technology solutions that span mobile apps, online crowdsourcing platforms, sensors, analytical and visualization technologies, and associated urban technologies. The paper puts forth several considerations that need to be accounted for when discussing the potential of data and technologies to transform our urban spaces towards the goals of making them intelligent, livable, sustainable, and resilient.