Actually...There is no cannon source that states the Romulans and Klingons are in the Beta Quadrant. The Beta Quadrant reference to the Romulans was first put forth in a novel, cant remember which one, but it has been picked up by many writers since then. And Star Trek VI mentions that the Klingons are in the Alpha Quadrant. (although they were very liberal with the term quadrant when TOS was involved.)
You must remember, There is a distinct difference between cannon and non-cannon, which can be summed up like this.
Cannon - All Television Episodes (minus TAS) and movies, and two novels (both written by Jeri Taylor, exec producer of Voyager)
Semi Cannon - Those ideas put forth off screen, notes from the film producers, blueprints created for ships. The Animated Series would fall into this category, in my opinion.
Non-Cannon- Anything put forth in a novel (minus the two Jeri Taylor novels), Techincal Manuals, etc.
Now of course, we can always go by the original definition of cannon as laid out by Gene Roddenberry, but to do so is more of a headache than its worth. The above is the official "What is cannon?" list put out by Paramount Pictures about three years ago.
The number of official maps in the Startrek universe could probably be counted on two or three hands...and only three of them deal with anything more than a star system or a few sectors. (If anyone can find that beautiful Stellar Cartography map from Generations that is probably the best one and is most likely to have some ideas for where everything is.)