For as long as data have been generated about cities various kinds of data-informed urbanism have been occurring. In this paper, I argue that a new era is presently unfolding wherein data-informed urbanism is increasingly being complemented and replaced by data-driven, networked urbanism. Cities are becoming ever more instrumented and networked, their systems interlinked and integrated, and vast troves of big urban data are being generated and used to manage and control urban life in real-time. Data-driven, networked urbanism, I contend, is the key mode of production for what have widely been termed smart cities. In this paper I provide a critical overview of data-driven, networked urbanism and smart cities focusing in particular on the relationship between data and the city (rather than network infrastructure or computational or urban issues), and critically examine a number of urban data issues including: the politics of urban data; data ownership, data control, data coverage and access; data security and data integrity; data protection and privacy, dataveillance, and data uses such as social sorting and anticipatory governance; and technical data issues such as data quality, veracity of data models and data analytics, and data integration and interoperability. I conclude that whilst data-driven, networked urbanism purports to produce a commonsensical, pragmatic, neutral, apolitical, evidence-based form of responsive urban governance, it is nonetheless selective, crafted, flawed, normative and politically-inflected. Consequently, whilst data-driven, networked urbanism provides a set of solutions for urban problems, it does so within limitations and in the service of particular interests.