Originally Posted by Wookieepedia
The Unknown Regions could be broadly defined as areas not connected with the skein of reliable or well-known hyperspace routes spanning the galaxy, did not look to Coruscant as the ultimate center of civilization, or were not under the broad hegemony of the Galactic Republic before the Galactic Civil Waróbut the full reasons behind this lack of contact remain unknown.
The depiction of the Unknown Regions varies from source to source. Some fans would like to limit the term to areas outside the plane of the galactic disk, and this hypothesis is not contradicted by any canon or EU evidence. It is supported by movie canon, which describes a Galactic Empire, and in which the entire galaxy can be surveyed for any lost planet, fugitive General Grievous, or Rebel base.
In Vision of the Future, the space known to the Old Republic, Empire, and New Republic is not specifically assigned to any section of the galactic disk, nor are the Unknown Regions. They do appear adjacent on the map, which includes the disk. The territory under the hegemony of the Empire of the Hand, while by no means comprising all of the Unknown Region, seemingly embraces as much as 240 sectors, roughly a quarter of the volume of known space. Although huge, this volume is emptier than the Galactic disk, since the combined total of the Unknown Regions contains no more than one percent of the galaxy's stars (Galaxy Guide 8: Scouts p24; Tales of the Bounty Hunters p301).
In contrast, the The Essential Chronology and New Jedi Order series, as well as the associated galactic map, have bulked the Unknown Regions on one side of the Galactic disk, and this seems now to be a geometric projection of sub-volumes above the disk (however, it should be noted that some fans subscribe to a two-dimensional interpretation, in which the Regions actually touch much of the disk). Worlds such as Kamino, lying "beyond the Outer Rim" on the opposite side of the galaxy, in a dwarf satellite galaxy 70,000 light years from the galactic center, might also be considered as lying on the edge of this zone.