The "Zheng He map" In January 2006, BBC News and The Economist both published news regarding the exhibition of a Chinese sailing map claimed to be dated 1763, which was stated to be a copy of another map purportedly made in 1418. The map has detailed descriptions of both Native Americans and Native Australians. According to the map's owner, Liu Gang, a Chinese lawyer and collector, he purchased the map in 2001 for $500 USD from a Shanghai dealer.Zheng HeAfter Liu read the book "1421: The Year China discovered the World" by Gavin Menzies, he realized the significant potential value of the map. The map has been tested to verify the age of its paper, but not the ink. Even though the map has been shown to date from a period that could cover 1763, the question remains as to whether it is an accurate copy of an earlier 1418 map, or simply a copy of a contemporary 18th-century European map.
A number of authorities on Chinese history have questioned the authenticity of the map. Some point to the use of the Mercator-style projection, its accurate reckoning of longitude and its North-based orientation. None of these features was used in the best maps made in either Asia or Europe during this period (for example see the Kangnido map (1410) and the Fra Mauro (1459). Also mentioned is the depiction of the erroneous Island of California, a mistake commonly repeated in European maps from the sixteenth to eighteenth centuries.
Geoff Wade of the Asia Research Institute at the National University of Singapore has strongly disputed the authenticity of the map and has suggested that it is either an 18th or 21st-century fake. He has pointed out a number of anachronisms that appear in the map and its text annotations. For example, in the text next to Eastern Europe, which has been translated as "People here mostly believe in God and their religion is called 'Jing'", Wade notes that the Chinese word for the Christian God is given as "Shang-di", which is a usage that was first coined by Jesuit missionaries in the 16th century.
In May 2006, it was reported by the Dominion Post that Fiona Petchey, head of the testing unit at Waikato University, which had carbon dated the map, had asked Gavin Menzies to remove claims from his website that the dating proved the map was genuine. The carbon dating indicated with an 80% probability a date for the paper of the map between either 1640-1690 or 1730-1810. However as the ink was not tested, it was impossible to know when it was drawn. Ms Petchey said, "we asked him to remove those, not because we were not happy with the dates, but because we were not overly happy with being associated with his interpretations of those dates."
A cursory examination suggests a glaring lack of scientific discipline pertaining to Menzies' book, more akin to Charles Berlitz.
You reference a map dated 1418. However, the voyages began in 1421 and return was in 1424. Therefore, the only logical conclusion if the 1418 date is correct, is that this was a map used by the 1421 explorers to further fill out their preliminary 1418 and other early information. I doubt an emperor would finance 800 or more ships based on pure speculation.