Prior research has pointed to worker interactions, technological innovation, and specialization as key sources of urban productivity gains but has been limited by the available data in its ability to fully characterize work across geographies. We study the sources of geographic inequality and present new facts about the geography of work using online job ads. We show that the (i) intensity of interactive and analytic tasks, (ii) technological requirements, and (iii) task specialization all increase with city size. The gradient for tasks and technologies exists both across and within occupations. It is also steeper for jobs requiring a college degree and for workers employed in non-tradable industries. We document that our new measures help account for a substantial portion of the urban wage premium, both in aggregate and across occupation groups.