Both nile and oasis are fine. I like 'oasis' because it is not specific to the nile river region. It could be southern spain, as in cordoba, the middle east, or polynesia.
I don't think calling Cordoba an oasis very is realistic.
Namely, palm trees are certainly not native to the Iberian peninsula (Portugal + Spain)! They can and have been grown (read "imported") to good looking specimens, most preferably in the southern part of the peninsula, though.
Also, I would not think the earth (or sand) would look that much alike, even at a distance.
No, there are no "oasis" in the Iberian pensinsula because there are no deserts here! Some arid areas yes, deserts no! Hence no oasis either.
Mediterranean is also not a good title - what I said above is just about a rather small part of the "shores" of the Mediterranean...
And it's definitely NOT like the Amazonia! You'd have nothing but trees and trees and more trees in such a tileset! lol
Nile sound good to me. Could possibly be Mesopotamia as well?... Not sure...
But if so, it be used with your Persians faction too, titi.
Anyways, titi, it's looking very good, just for the pics I've seen on the topic - if it's improved since, all the better!
EDIT: Finished a sentece I hadn't finished before.