The diachronic projection: past and future movements of hydrographic systems on early modern maps

To this day, the Mercator projection allows cartographers to flatten the three-dimensional world onto two-dimensional paper. As this article shows, Mercator’s was not the only cartographic innovation pioneered in the early modern period: contemporary hydraulic experts routinely included the fourth dimension, time, in their maps. Capturing past movements of water, such as floods, but also future ones, such as planned land reclamation, required the development of a visual language allowing several temporalities to coexist within the same space. Early modern hydraulic experts can thus be said to have developed the diachronic projection. As well as allowing for the reduction of four dimensions onto two, this captured affects and desires on paper by combining depictions of the undesired (floods) and the desired (land reclamation). Given the recent interest for the history of projects, and the reframing of the early modern period as a projecting age, this article argues that it is time for scholars to recognise the importance of the diachronic projection.