Not so fast.

I'm no cartographer, and I don't study the history of Chinese exploration, but I'm not buying this map that purports to be a 1763 copy of a map drawn in the year 1418. It's believed by some to substantiate the claims made in Gavin Menzies' 1421: The Year China Discovered America.

Why am I skeptical?

Who in 1418 could have sailed the seas so extensively as to map the coast lines of every major land mass on the globe, including dozens of major islands, and even antarctica?

But aside from the manner of representing water, which any forger would imitate, it looks nothing at all like any Chinese maps I've been able to track down. (Cf. these, found online at the Honk Kong Baptist University.)

Here's a pretty good example from 1602, which shows that chinese cartographers knew the world well enough by then.

One might object that in the '1418' map California appears to be a large island, but this should be the entire west coast from the peninsula of Baja California in Mexico to Vancouver Island in Canada. In all the time it would have taken to travel that coast line, who could imagine that Alert Bay was connected to the Gulf of California? This seems like the kind of thing a forger would do, to give the impression that something was seen but not explored.

But then again, what does it matter? Do you really care if an Italian didn't see America before a muslim sailor from China? How exactly does that radically alter history? Unless he yelled 'dibs.'