南極圏
The Arctic Circle is roughly long, as is the Antarctic Circle. A "true circumnavigation" of the Earth is defined, in order to account for the shape of the Earth, to be about 2.5 times as long, including a crossing of the equator, at about . On the flat Earth model, the ratios would require the Antarctic Circle to be 2.5 times the length of the circumnavigation, or 2.5x2.5=6.25 times the length of the Arctic Circle.