I get the feeling that these areas really weren't designed from the ground up as actual places. Rather, when I look at the Coerthas main map, I get the feeling that these "areas" are a collection of square-shaped map tiles that have been laid side by side. Some of the tiles were rotated, and some were edited a little, and then they were dropped down alongside each other. Plop enough of them down, do a little more editing, and voila!: a field map.
That's how about every games are created.
What FFXIV hasn't done is re-using the same 3D objects with different textures (heavily used in FFXI, for example ; less complaints because players are more focused on textures than 3D objects) and it seems there is only 1 layer of tiles in FFXIV (2 layers should be a minimum - ground + objects like trees, houses, etc. - which allow more variety with composition)