This essay examines the geographical production of the Virreinato del Río de la Plata and the formation of its northern frontier with Brazil. I use the work of Félix de Azara to demonstrate how he and other cartographers transformed the administrative apparatus of the viceroyalty into a spatial enterprise. I argue that mapping was an integral technique of colonial governance that engendered material consequences, and that the spatial vision of the viceroyalty was challenged even in the process of its reproduction. The essay is broken into four parts. In the first two, I examine the overlapping and mobile patterns of human settlement along the interstate borderlands and how Azara negotiated and abstracted them to create readable maps. The third section focuses on resettlement programs that Azara oversaw to populate the frontier, while the fourth provides a close reading of the maps and natural history that he published of the region.