[Sherman Logan]

A copy of a 1418 Ming map, said to have been found in a Shanghai antique shop by Beijing antiquities scholar Liu Gang, is held up by Gunnar Thompson as evidence that Asian explorers sailed the world long before Columbus. Critics doubt the map is authentic.

I'm with the critics. That is an awfully good map for 1418. Beats European maps by two or three centuries.

While the Chinese could probably figure latitude okay, they certainly couldn't figure longitude accurately, since they didn't have chronometers. Accurate maps without good chronometers and many observations is just not possible.

[Jedi Master Pikachu]

It also strongly suggests that the world is a sphere. Although some people had this idea (such as the Greeks), the standard idea at the time was a flat world.