It is my opinion that the lower part of the map represents Terra Australis Incognita and in particular the northern coast of Vietnam. The important gulf on the left is Tonkin Gulf. Probably the missing part of the map reached Thailand.
In particular the shape of the map in this part is a orizontal devepolment of coasts and corresponds with mythical Terra Australis.
Another possible interpretation may bring to Thailand
Terra Australis in Piri Reis' map
At the bottom Terra Australis in the map of Lopo Homem (1519)