Antarctica was a continent encompassing the southern-most area of the Earth, including its south pole.
In the late 17th century, a cartographer created a map, from what was learned from European explorers and traders, of the lands that had coastlines on the Indian Ocean and Arabian Sea. Although Antarctica was unknown at this time, he included in his map a land called "Terra Austr Incognita" south of Nova Hollandia. This was centuries before humans discovered and explored this continent. (Star Trek: Enterprise, opening credits)
The 17th century map, known as "Harmonia macrocosmica seu atlas universalis et novus, totius universi creati cosmographiam generalem, et novam exhibens", was created by Andreas Cellarius. The Antarctic Circle was depicted as running through this land. A scan of the original can be found here
The map used in the remastered "The Cage" was a Central Intelligence Agency map published either in April 2007  or September 2008 . The difference, which was not noticeable at the resolution of the image from the episode, was the addition of Kosovo, which gained its independence between the releases.