Frontiers became increasingly central to colonial spatial sciences as the nineteenth century progressed. Examining surveyors’ activities in the field along with the material processes by which maps were produced and circulated, this chapter analyses three broad junctures of frontier surveying based on distinct techniques of seeing and representing space. Route surveys of the 1820s to 1840s mostly gave way to triangulation from the 1850s on, and trigonometrical survey parties increasingly ventured into frontier regions from the later 1860s. By this later period, surveyors and ‘men of science’ in metropole and colony alike deemed comprehending frontier locales a key goal of imperial science. Agents of empire considered these regions as providing unparalleled opportunities, but also substantial challenges to established modes of spatial knowledge and representation. The chapter shows how this ambiguity reached a peculiar resolution, as many surveyors and geographers came to celebrate and to uphold the elusive quality of India’s frontiers.