Terra Australis is the large continent on the bottom of the map

Terra Australis (more completely Terra Australis Incognita, "(the) unknown southern land") was an imaginary continent, appearing on European maps from the fifteenth to the eighteenth century.

It was first introduced by Ptolemy, a Greek cartographer from the first century AD, who believed that the Indian Ocean was enclosed on the south by land. When, during the Renaissance, Ptolemy became the main source of information for European cartographers, the land started to appear on their maps. Although voyages of discovery sometimes did reduce the area where the continent could be found, cartographers kept drawing it on their maps and scientists argued for its existence with such arguments as that there should be a large landmass in the south as a counterweight against the known landmasses in the Northern Hemisphere. Usually the land was shown as a continent around the South Pole, but much larger than the actual Antarctica, spreading far north in particular in the Pacific Ocean area. New Zealand, discovered by Abel Tasman in 1642, was by some regarded as a part of the continent as well as Africa and Australia.

Map of Terra Australis

The idea of Terra Australis was finally corrected by James Cook. On his first voyage he circumnavigated New Zealand, showing it could not be part of a large continent. On his second voyage he circumnavigated the globe at a very high southern latitude, at some places even crossing the south polar circle, showing that any possible southern continent must lie well within the cold polar areas, and not in regions with a temperate climate as had been thought before.