Marco Polo's book, The Travels of Marco Polo, describes places of which Polo had firsthand knowledge, and other places of which he had no personal experience. Three of the places described by Polo which he did not visit are: a large island he calls Zenzibar, the province of Lochac (Beach), and the kingdom of Malaiur (Maletur). This paper looks at the mapping of the three by Gerard Mercator, his trust in Marco Polo, and his irregular use of map legends. It includes a discussion of the promontory of Mercator's southern continent, depicted on his 1541 globe and 1569 world map, which extends north of the Tropic of Capricorn, south of Java Major. In an inscription on his 1569 map, Mercator stated his sources for the depiction as Marco Polo and Ludovico di Varthema. The paper considers whether there were other influences and concludes that the inscription is not all-encompassing.