The Philadelphia Print Shop has a page on mythical geography in antique maps: Illusions, Confusions and Delusions.
Old maps are filled with inaccuracies — rivers running a wrong course, cities placed incorrectly, coastlines lacking bays, and mountains, lakes and islands missing completely. The mistakes in old maps are one of the primary aspects which makes them interesting to us, and much of the history of cartography is the history of the correction of these errors. One category of cartographic error consists of what are called “geographic myths.” These are geographic features that appear on the map but not on the earth; cities where none ever were, islands where there are but waves, lakes and rivers where there is dry land, and kingdoms of non-existent kings. Geographic myths populated most areas of the world and the history of exploration is filled with expeditions in search of chimeras that existed only on the map.