Check this out: jump.
In summary, there’s a LOT of land mass built into Skyrim and the purpose isn’t immediately clear. My gut tells me it’s there for future DLC; as that poster theorized, much of the land mass is likely there for “distant views from the clouds”. (Not a real quote; a finger-quotes paraphrasing. Go read the article. <3) He asks then why there are chunks of land mass that are both underdeveloped and completely impossible to see – even as distance geography – from the current traverseable map?
The only thing he doesn’t mention is the degree of expansion; consider that if DLCs bump explorable terrain out further from the current map that more things will become visible in the distance…things that are already built-in. His other theories (straight up DLC, presence for the modding community, etc.) are just as plausible.
Regardless of the reason, the level of effort put in is both a nice touch and a good sign.