The Mystery Of Extraordinarily Accurate Medieval Maps

One of the most remarkable and mysterious technical advances in the history of the world is written on the hide of a 13th-century calf. Inked into the vellum is a chart of the Mediterranean so accurate that ships today could navigate with it. Most earlier maps that included the region were not intended for navigation and were so imprecise that they are virtually unrecognizable to the modern eye.
These beautifully detailed portolan charts present historians with a puzzle: How were they made? A mathematical analysis offers some clues.