The ubiquity of sensors, mobile devices and crowdsourced services, notably in urban environments, has led to an explosion in the volume of data sets that have both spatial and temporal components. These data are also a rich source for domain scientists who aim to better understand cities and their populations. If properly acquired, integrated, and analyzed, “big data” can enable better operations, informed planning, and improved policy in cities. In this talk, I will discuss the challenges in visual exploration of big urban data sets through technological advances in large-scale data management and visualization. I will demonstrate our key contributions in two practical use cases in New York City.