Wikipedia on the Maps of Columbus:
Europe had long enjoyed a safe land passage to China and India—sources of valued goods such as silk, spices, and opiates—under the hegemony of the Mongol Empire (the Pax Mongolica, or Mongol peace). With the Fall of Constantinople to the Turkish Ottoman Empire in 1453, the land route to Asia became more difficult. In response to this the Columbus brothers had, by the 1480s, developed a plan to travel to the Indies, then construed roughly as all of southern and eastern Asia, by sailing directly west across the "Ocean Sea," the Atlantic Ocean.
Washington Irving's 1828 biography of Columbus popularized the idea that Columbus had difficulty obtaining support for his plan because Europeans thought the Earth was flat. In fact, the primitive maritime navigation of the time relied on the stars and the curvature of the spherical Earth. The knowledge that the Earth was spherical was widespread, and the means of calculating its diameter using an astrolabe was known to both scholars and navigators.
Diameter of Earth and travel distance estimatesA spherical Earth had been the general opinion of Ancient Greek science, and this view continued through the Middle Ages (for example, Bede mentions it in The Reckoning of Time). In fact Eratosthenes had measured the diameter of the Earth with good precision in the 2nd century BC. Where Columbus did differ from the generally accepted view of his time is his (very incorrect) arguments that assumed a significantly smaller diameter for the Earth, claiming that Asia could be easily reached by sailing west across the Atlantic. Most scholars accepted Ptolemy's correct assessment that the terrestrial landmass (for Europeans of the time, comprising Eurasia and Africa) occupied 180 degrees of the terrestrial sphere, and dismissed Columbus' claim that the Earth was much smaller, and that Asia was only a few thousand nautical miles to the west of Europe. Columbus' error was attributed to his insufficient experience in navigation at sea.
The true circumference of the Earth is about 40,000 km (25,000 sm), a figure established by Eratosthenes in the 2nd century BC, and the distance from the Canary Islands to Japan 19,600 km (12,200 sm). No ship that was readily available in the 15th century could carry enough food and fresh water for such a journey. Most European sailors and navigators concluded, probably correctly, that sailors undertaking a westward voyage from Europe to Asia non-stop would die of thirst, scurvy or starvation long before reaching their destination. Spain, however, having just completed the expensive Reconquista, was desperate for a competitive edge over other European countries in trade with the East Indies. Columbus promised such an advantage.
Europeans generally assumed that the aquatic expanse between Europe and Asia was uninterrupted. While hints of the American continent about Vinland were already surfacing in Europe, historians agree that Columbus calculated a too short distance from the Canary Islands to Japan by the standards of his peers.
Trade windsThere was a further element of key importance in the plans of Columbus, a closely held fact discovered by or otherwise learned by Columbus: the Trade Winds. A brisk westward wind from the east, commonly called an "easterly", propelled Santa María, La Niña, and La Pinta for five weeks from the Canary Islands off Africa. To return to Spain eastward against this prevailing wind would have required several months of an arduous sailing technique upwind, called beating, during which food and drinkable water would have been utterly exhausted. Columbus returned home by following prevailing winds northeastward from the southern zone of the North Atlantic to the middle latitudes of the North Atlantic, where prevailing winds are eastward (westerly) to the coastlines of Western Europe, where the winds curve southward towards the Iberian Peninsula. So he used the North Atlantic's great circular wind pattern, clockwise in direction, in both legs of his voyage.
The strange coincidence of there actually being land where some of the maps Columbus was using said there would be land (as in the composite above, maps taken from just before and just ater Columbus' journey and mentioned by name in earlier parts of this series) has struck many people as not coincdental at all, and in fact as downright suspicious. And in fact what is shown here is the way the Atlanteans (through the Egyptians and finally through Plato) described the situation. Quoting Donnelly about this below:
Atlantis, the Antediluvian World, by Ignatius Donnelly, ,
Chapter IV, "Corroborating Circumstances" p. 172
4. Plato says that there was a "passage west from Atlantis to the rest of the islands, as well as from these islands to the whole opposite continent that surrounds that real sea." He calls it a real sea, as contradistinguished from the Mediterranean, which, as he says, is not a real sea (or ocean) but a landlocked body of water, like a harbor.
Now, Plato might have created Atlantis out of his imagination; but how could he have invented the islands beyond (the West India Islands), and the whole continent (America) enclosing that real sea? If we look at the map, we see that the continent of America does "surround" the ocean in a great half-circle. Could Plato have guessed all this? If there had been no Atlantis, and no series of voyages from it that revealed the half-circle of the continent from Newfoundland to Cape St. Roche, how could Plato have guessed it? And how could he have known that the Mediterranean was only a harbor compared with the magnitude of the great ocean surrounding Atlantis? Long sea-voyages were necessary to establish that fact, and the Greeks, who kept close to the shores in their short journeys, did not make such voyages.
This is my earlier map showing my estimations for the Maps of the Ancient Sea Kings. The white area would be well-known and well0-charted bythe Atlantean Sea Kings, and they would be well aware enough of the continental/land area shown in paler grey. The other parts of the world are excluded and would have been mapped separately. Atlanteans knew of a Bering Land bridge and presumably when they settled in America they met overland travellers coming from the other way around. The white ara sould continue up to the point of Brazil as well. Note that going by this, the mapping of Antarctica (if any) would have come from other sources.
This is my new suggested map for the Sundaland Ancient Sea Kings, ca 10000-15000 years ago. in this case the green area is the homeland and well-known to them. The lighter grey areas are more vaguely known and if we allow that Churchward was telling the truth about his Tibetan rock art atlas, the Americas would also count in this category. The lighter blue seas were more familiar to them, including the areas around Antarctica. at the time there would be dense pack ice and giving the illusion that the two landmasses were connected: also there was extensive pack ice around much of the rest of Antarctica giving the illusion it was much larger (at the same time the glaciers were not in the same place we have Antarctic ice today and there could have been large aeas of exposed unglaciated land. And my presumption has always been that the particular attraction to Alaska was in its breeding grounds for whales: the tall ships of this era must have included whalers.