In the 13th century, so-called “portolan maps” appeared that are so accurate, they could be used in navigation today. But it has been a mystery how they were made and how, given the limits in technology of the time, they could be so accurate. (This is another example of how the notion that people from other times were unintelligent is just untrue, as in the myth that people in the Middle Ages thought the earth was flat.) A mathematician has figured out at least part of the answer of why these hand-drawn maps are so good, with even their limitations pointing to a startling sophistication.
From Julie Rehmeyer, The Mystery of Extraordinarily Accurate Medieval Maps | DiscoverMagazine.com:
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.