This Mod adds the 'Larger' (about 40% bigger than 'Large') and 'Huge' (about twice as big as 'Large') terrain size and some more terrain options: Swamp, Caldera, Plains, Big Lake, Flooded Plains and Waterworld. 
WARNING: The "Huge" terrain is known to sometimes produce water texture glitches. "Larger" should be safe. 

Swamp: 
A flat terrain with lots of small, often overlapping lakes  

Plains: 
A very flat terrain with only a few small hills around 

Big Lake:
Very flat terrain with a big lake

Caldera: 
A big round and very flat crater with a lake, surrounded by mountains 

Flooded Plains: 
Few flat pieces of land, surrounded by a lot of water

Waterworld: 
A lot of water, containing some islands


This mod can conflict with similar terrain mods. 

You can find this mod on steam as well:
http://steamcommunity.com/sharedfiles/filedetails/?id=345803966


Changelog v6:
- 'Big Lake' got missed last version, this time it is listed again
- Large, Larger and Huge 'Plains' maps are flatter now
- 'Crater' is called 'Caldera' again and is listed now, minor changes to the 'Caldera' code