Good find, it spurred me to llok up information on this map and I cam across this website:

http://www.uwgb.edu/dutchs/pscindx.htm

The Links in particular are under Catastrophes and Other Marvels where he talks about the 1421 Chinese Map, ancient Korean maps, and the Piri Reis map.

Thanks for helping me learn more about our wonderful history of Cartography. Have some Rep!