Sectors are divided into Sub-Sectors, which range from ten to twenty light years in diameter. Sub-Sectors, rather than being general blocks of space like sectors, are instead centered on densely populated star clusters, important worlds, or meeting points of warp trade routes. Each Sub-Sector is often made up of multiple Systems with the most significant and, often, prosperous Systems being the Governoring System.
The areas between sectors and subsectors are vast, in fact making up more of the Galaxy than the Imperium controls. They are often unexplored, uninhabited, alien empires, or inaccessible by the warp. These zones are known by various names including Wilderness Space or wilderness zones, inter sectors, forbidden zones, empty space, or frontier space.