A Sector is an Imperial division of space that is one of the constituent territorial units of a Segmentum of the Milky Way Galaxy. The size of a sector varies according to local demands and stellar density. A typical sector might encompass 7 million cubic light years, equivalent to a cube with sides almost 200 light years long. Sectors are divided into sub-sectors, usually comprising between 2 and 8 star systems within a 10 light year radius (some may encompass more systems - others only 1). This size is governed by the practical patrol ranges of Imperial starships. Because sub-sectors are divisions of worlds (rather than volumes of space) there are vast numbers of star systems within each sector which do not fall with in a sub-sector. These are referred to as inter-sectors - and are commonly better known as wilderness zones, forbidden zones, empty space and frontier space. Inter-sectors may contain gas or dust nebulae, inaccessible areas, alien-inhabited star systems, unexplored systems, uninhabited systems and uninhabitable worlds. Each sector has an Imperial Navy Battlefleet assigned to the task of safeguarding it, and the Battlefleet is generally named after the sector it is assigned to (Battlefleet Gothic is located in the Gothic Sector, Battlefleet Cadia is located in the Cadian Sector, etc).
- Battlefleet Gothic Rulebook, pg. 86
- White Dwarf 139, "Interstellar Travel"
- White Dwarf 140, "Interstellar Travel"