In his bestselling novel from 2005, Die Vermessung der Welt (Measuring the World), Daniel Kehlmann brings together the explorer Alexander von Humboldt and the mathematician Carl Friedrich Gauss in an effort to show that the scientific progress preached by the Enlightenment is a double-edged sword. Hence the double entendre of the title: Humboldt's and Gauss's “surveying” (Vermessung) enterprises typify human “arrogance” (Vermessenheit) toward nature. The ideas presented in Kehlmann's book were no doubt influenced by Thomas Pynchon's Mason & Dixon (1997), a metafictional history in which the Mason and Dixon survey is represented as a rationalist endeavor that transforms the primitive American landscape into an organized grid of human control. Both authors are critiquing, from a postmodern vantage, eighteenth-century instrumental reason, which manifests itself in the urge to measure, chart, and demarcate the world. At various points in his narrative, Pynchon sums up this basic anthropocentric view as mathesis, a term that recalls the early modern scientific project of mathesis universalis or the attempt to “mathematize” nature. According to Heidegger, mathesis, which sums up our modern technological attitude toward the world, developed as a result of Galilean geometry, Newtonian science, and Cartesian philosophy, all of which conceptualize reality according to purely speculative mathematical laws. This article brings Heidegger, Pynchon, and Kehlmann into dialogue with one another in an effort to show how they each critique, in remarkably similar fashion, the conceptual as well as physical lines of demarcation that mathesis inflicts upon the world.