How Medieval Maps Were Made So Accurate

[HammerStone]

If you're interested in geography, mathematics or history, this is pretty darn interesting!

http://discovermagazine.com/2014/june/14-the-mapmakers-mystery

That first portolan mapmaker also created an enormous puzzle for historians to come, because he left behind few hints of his method: no rough drafts, no sketches, no descriptions of his work. “Even with all the information he had — every sailor’s notebook, every description in every journal — I wouldn’t know how to make the map he made,” says John Hessler, a specialist in modern cartography at the Library of Congress.