This blog entry is going to be short and it is going to be a rant, so fair warning.
In the Star Wars universe, the 'Unknown Regions' were first introduced (I believe) during the Heir to the Empire trilogy. Grand Admiral Thrawn was said to have commanded a fleet in this region in the late stages of the Rebellion—and thus was not around to thwart the Alliance after the Imperial defeat at Endor. The exact location of the 'Unknown Regions' was never detailed in this book, and I was fine with that. I figured it was somewhere at the edge of the galaxy, beyond the outer-rim. That would make sense, as not too many travel out further than the outer rim.
And then the map came out—I believe it's first appearance was in the crappy 'Vector Prime' novel. And there, it is revealed that the Unknown Regions are actually... the other half of the Galaxy. You know, the left half. As opposed to the right half, where all the cool planets are.
This never made a bit of sense to me. Especially when you consider the proximity of Coruscant and other major core worlds to the Unknown Regions. I mean, its like the first explorers just decided not to turn left...for...10,000+ years, they just.. decided not to turn left. Oh sure, there are billions of planets in (relatively) close proximity to Coruscant, but we're just not going to go that way in favor of pushing out further and further to the 'right'.
And there is no explanation (that I've heard of) as to why half the freaking galaxy is unexplored. Nor could there be any sensible one. This is a prime example of the stupid part of the Expanded Universe—and this from a person who is really TRYING to like the EU.
I had always assumed that the Republic and the Empire actually DID rule over the entire 'Galaxy'—oh sure, not all parts of it, and especially not the less explored outer and 'unknown' regions, but the majority of the galactic disc at least. And in my campaign, that's how it is (and that's one of the reasons one of my projects is to revamp the Galaxy Map).