Entire departments of the Adeptus Administratum are devoted to cataloguing the worlds in the EmperorвЂ™s domains, a never-ending task, for it is in a state of eternal flux. No one has ever been able to map all of them and no one can truly even say how many there are beyond the figure of 1,000,000 normally cited above. The Imperium encompasses countless worlds. These unexplored depths harbour all many of terrors, from ravening pirates to unknown alien empires, as well as untold riches, from long-lost human colonies to worlds strewn with the wealth of long-extinct xenos species. These sectors are connected to one another by relatively stable, if still hazardous, inter-sector Warp routes and the vast, uncharted reaches between each are referred to as Wilderness Space. Worlds once colonised because of their location or some desirable natural resource have developed into the cores of sectors, many of which have swollen to include two hundred or more star systems. Instead of being scattered at random, the worlds of the Imperium are clustered around areas settled during the lost age of MankindвЂ™s first great wave of expansion into the galaxy during the Age of Technology. While it is true that some governors rule not just a single planet but an entire star system, and that other worlds have no governor at all, the fact is that the Imperium is stretched so thinly across the void that an interstellar traveller could make his way from one edge to the other, traversing a hundred thousand light years of space, and not once cross paths with a human being. The volume of space claimed in the name of the Emperor of Mankind contains hundreds of millions of stars, many host to their own planetary systems, and yet there are only an estimated million or so Planetary Governors occupying the thrones of the ImperiumвЂ™s worlds. The Imperium of Man is spread impossibly thin across an estimated two-thirds of the entire Milky Way Galaxy.

The Adeptus Administratum of the Imperium generally classifies all planets in the galaxy according to the following classifications for the purposes of raising tithes of raw materials, manufactured products and Imperial Guard regiments.

Most of these worlds were settled by humans many centuries before the Great Crusade of the 31st Millennium reunited the human colony planets beneath the rulership of the Emperor of Mankind, though thousands more have been settled in the ten millennia since then by Imperial colonists. The Imperium of Man is home to over 1,000,000 human-settled planets scattered across over 100,000 light years of space in the Milky Way Galaxy. The Milky Way Galaxy in the late 41st Millennium AD ' You cannot fathom the mysteries of the Universe, you must simply trust in the righteousness of the Emperor's Command.'

The imperial guard song