Maps in the European and Muslim world up to this time and for about a century afterward displayed Africa with its lower half pointing toward the East.
Section of Mongol Atlas of 1320, notice correct orientation of Africa
Section of Vesconte Atlas of 1320 with bottom half of Africa pointing toward the East
Where did the Chinese geographer get his information on Africa? The voyages of Zheng He did not start until nearly a century after Chu Ssu-Pen's atlas was published.
He did not get his information from Europeans or Muslims since his maps do not show similar morphology. The other people dealing in trade with Africa were the Nusantao merchants of Sanfotsi and Toupo. Interestingly, Chu Ssu-Pen actually mentions informants in his notes:
Regarding the foreign countries of the barbarians southeast of the South Sea, and northwest of Mongolia, there is no means of investigating them because of their great distance, although they are continually sending tribute to the court. Those who speak of them are unable to say anything definite, while those who say something definite cannot be trusted; hence I am compelled to omit them here.
The author states here that he rejects information of areas southeast of the South Sea (South China Sea) and northwest of Mongolia. However, what about informants from other areas?
If we believe Galvão then a map existed as early as 1428 showing the Straits of Magellan in South America. Gavin Menzies explains this as coming from the master chart of Zheng He whom he claims circumnavigated the globe on his treasure voyages.
Again much of the evidence Menzies uses to support this idea is identical with that used by Heyerdahl in his "American Indians in the Pacific" theory. Actually, Heyerdahl suggested that it was bearded trans-Atlantic "Nordics" from America rather than Amerindians who made the Pacific voyages.
A great deal of this evidence can easily be shown to predate the Ming period. For example, the ruins at Ponape in Micronesia mentioned at Menzies site are dated more than a millennium before Zheng He's voyages.
However there is one interesting bit of Ming period evidence cited by Menzies. The discovery of a junk in the Philippines off North Pandanan Island by Dr. Eusebio Dizon uncovered a store of metates in the hold. Zhu Di coins date this junk to about 1421.
A metate "mortar" -- corn was ground into the central hole
Metates are grinding stones used in pre-Columbian America. The metates found in the junk were similar to those used in South America. We should note that the Chinese name Lusung may be a transliteration of a local word in the Philippines meaning "mortar" as in "mortar and pestle."
While I can't trace specifically how Nusantao traders would have come to know about the Straits of Magellan, it might be helpful to follow what I call the "tumbaga trail." As mentioned earlier, tumbaga is a copper alloy, usually copper and gold. The word "tumbaga" in nearly the precise same form is found in the Philippines and in different areas of the Americas.
From Peru, tumbaga spread into Argentina and Chile and northward into Columbia. It was found in Mexico, in the Caribbean and in other areas of the Americas. However, it was not always found with the name "tumbaga" or its derivatives.
This expansion of metallurgy was undoubtedly due to the spread of indigenous cultures and empires. However, if we believe in rather regular Nusantao contacts with the Pacific coast of the "New World," we can expect that, like any good explorer/merchant, they would have expanded their "tree" of contacts thoroughly.
It is interesting to note that none of the maps suggested by Menzies to show the Americas, with the possible exception of Kublai Khan chart, are found in China. We take here that the Kublai Khan chart mentioned is based on the idea that a map found in 1911 in the Balkans came from a source map produced in Samarkand. It is therefore speculative that this chart came from Kublai Khan's court.
Such a scenario would make sense from the Nusantao perspective we have suggested here. For China to get involved in the spice trade, it makes no sense to sail eastward around the world to get to the Indian Ocean. However, for Europe sailing westward to this region was a viable alternative to sailing around the continent of Africa, especially from the point of view of trade winds and currents.
Paul Kekai Manansala
Evidence on Pandanan junk and metates presented by Dr. Eusebio Dizon at Royal Geographical Society on March 15th, 2002.
The Mongol Atlas (Kuang Ku Tu), http://www.henry-davis.com/MAPS/LMwebpages/227mono.html