After the Compass and Before the Chart: Considerations on the Origin of the Portolan Chart by Gregor

The origin of the medieval portolan charts, which have been called the “first true maps,” is shrouded in mystery. Historians of cartography have long struggled with vexing questions about who, how, when, and from where these modern-looking charts came. In my presentation I will comment upon the apparent confusions made by some researchers between “accuracy” and “precision”, and between two different measurement systems – one used for making the charts and another for studying the charts. I will then suggest what technologies had to be present in the 13th century in order to give rise to the creation of the portolan chart. Finally, given that the primary function of the chart in plotting courses, I offer my idea that the precursor to the portolan chart did not start out as a map but as a piece of scrap parchment for calculating the sides of triangles for recovering the course.