@Keith Although the maps do not prove anything intrinsically, do remember that cartographers used to be taken very seriously. Selling an explorer a bad map could cost your reputation, your career, and maybe even your life if the poor guy ever returned home to pay you back for making a bad map which nearly got him killed. So a well-respected mapmaker, like Mercator and others shown in the video, would not have made a bogus map merely for the fun of it. It was an expensive endeavor back then, not to mention extremely difficult.