The drawing is showing 30km, I remember that cry engine was only doing 4km by 4km.
So the engine is doing 15km by 15km, but then he has stuff outside the 30km square to?
https://twitter.com/sj_sinclair
Warframe is using UE4, not CryEngine.
UE4 supports up to 500 units in any direction. Each unit can be what you want it to be e.g. at 1 unit = 10mm, you would end up with a max scene size of 5000mm (or 5m).
Also, the recommended UE4 max map size is 20km in any direction; but you will start having physics issues after about 5km size. That's why to build a large map, you have to split it up into chunks, then stream it.
However, UE4 also supports dynamic origin shift (they call it world rebasing) - which is too technical and complex for me to explain. But basically, that, in conjunction with the UE4 streaming capability, you can basically have any map size you want.
Basically, to UE4, a 30km x 30km map size is nothing.
ps: Steve used to work for me before he went to DE, where he's been since.