My interpretation

Oriental coasts of Asia on the left and at the bottom ( very similar to Piri Reis'  map)

All pictures are taken from internet

Columbus' Map: on the left oriental coasts of Asia

Cantino's world map: on the left oriental coasts of Asia

Rosselli's world map: Asia at the bottom (Terra Australis Incognita)

The question is WHY?

An ancient map of Asia

Terra Australis Incognita at the bottom: it is Asia

Oriental coasts of Asia at the bottom: Terra Australis Incognita of Fianeus

In the first two images below it is possible on the left side to detect, yet again, (as in Piri Reis' map) the coasts of East Asia.  

In the successive maps it is possible to see in the lower part the Terra Australis Incognita.

It is my opinion that this huge land, the unknown land of the South, represents the entire oriental coasts of Asia from approximately Russia to Thailand.

The large island which appears on the right of some of the maps is probably Japan.