Imperium of Man - The Imperial Demesne: The territory of the Imperium is defined by the reach of the psychic beacon of the Astronomican, which has a range of approximately 50,000 light years. The Imperium proper could thus be thought of as a sphere whose center lies at Terra's Sol System, and whose radius is about 50,000 light years wide. However, as a practical matter, agents and agencies of the Imperium (along with "unofficial" representatives of the Imperium -- such as Rogue Traders -- who often work in tandem with the goals of the Imperium) carry on its affairs and expand its influence beyond that limit. The disparate and widespread nature of Imperial territory, with its millions of star systems and worlds, means that a strongly centralised government would be unfeasible.The Imperium encompasses countless worlds. No one has ever been able to map them and no one can even say how many there are. Entire departments of the Adeptus Administratum are devoted to cataloguing the worlds in the Emperor's domains, a never-ending task, for it is in a state of eternal flux. Furthermore, the Adeptus Terra holds that the whole Human species and the entire galaxy are under the Emperor's rule -- the Imperium has a manifest destiny to unite Mankind, impose its laws on every Human world and destroy all alien life. The true scope of the Imperium is, therefore, the entire galaxy, though this is far from actuality. The Imperium jealously guards its territory whenever it can but its sheer size means that it cannot react to every circumstance. Many planets live and die alone, with only the truly great threats commanding the attention of the Adeptus Terra. Worlds are frequently lost to aliens, rebellion or disasters, with news of their destruction sometimes taking centuries to reach Terra. The Imperium's borders undergo constant change, with new worlds discovered, conquered or colonised and old ones lost to xenos attack, Exterminatus or even to the Warp.The Imperium of Man divides the galaxy into five administrative zones called Segmentae Majoris, which include the:Segmentum Solar, the galactic "centre," with the Sol System at its heart.Segmentum Pacificus, the sparsely-settled galactic "west."Segmentum Obscurus, a region to the galactic "north" of Terra that has been heavily fortified by the Imperial Navy and the Astra Militarum due to the dangers posed by this Segmentum's most infamous element, the Eye of Terror. This is a vast Warp rift where the Immaterium actually intrudes upon material space -- as do the Chaos Space Marine Traitor Legions and the daemons of the Ruinous Powers themselves.Segmentum Tempestus, the galactic "south."Segmentum Ultima, the largest province of all in the Imperium, located to the galactic "east" of Terra; its furthest extents are beyond even the range of the Astronomican in Wilderness Space still unexplored by Humanity.The Segmentae are the primary administrative divisions of the Imperium. Each is divided into sectors, which are areas of three-dimensional space. The sectors in turn consist of sub-sectors, each containing a number of individual star systems. These spatial divisions and subdivisions are also levels of the administrative hierarchy.Each Segmentum Governor (or Segmentum Commander, the term used when the governor is acting in his military capacity) oversees his Sector Governors (or Sector Commanders), who in turn oversee Sub-sector Governors (or Sub-sector Commanders), who in their turn oversee the individual Planetary Governors, who are also known as Imperial Commanders. The higher ranks in this administrative system are usually combined with a basic planetary governorship as well as interstellar duties. Each of these governors is usually a member of the Imperial nobility and it is rare, but not impossible, for a man or woman born in the lowest ranks of Imperial society to rise to the rank of an Imperial Governor on his or her own merits or abilities rather than inherit the role. This neo-feudal system is the means by which the Imperium maintains control of the separate planets that comprise it.