Before the time of the Red Empire, before the True Emperor and to an extent his father before him united the peoples of the galaxy under their rule, there was a system of navigation amongst the stars based on something other than Imperial territory – as modern Imperial navigation is today.
The Classic or Pre-Imperial Navigation system was founded on the basis that it was “Destination-Based” and followed a simple set of rules.
A heading would typically take the format of three sets of digits combined together, in the format xxxx-xxxx-xxxx, or x-y-z. The starting point on the three-dimensional co-ordinate graph would always be 0000-0000-0000.
The first set of co-ordinates would be on the first plane out, measured in ISUs (Interstellar Units) and would describe a distance through the number – for example 1540 ISUs on one plane.
The second set would add the second dimension, describing the distance again – for example 0951 ISUs out on the next plane.
The third set would add the third dimension, describing the distance one final time – for example 5999 ISUs out on this plane.
It would provide a heading for the ship or object travelling, as well as a length of distance to the target destination. It also varied depending on where the ship was located, and which direction it was pointing in. If co-ordinates or headings were being given between ships, the starting destination for calculation purposes would always be Earth, and then a separate set of co-ordinates would have to be calculated for the travelling ship.
Segmentation of the Colonised Galaxy and Imperial Navigation
If a three-dimensional graph of the colonised galaxy were displayed, it would show a badly-distorted ball of explored and colonised solar systems, not quite centred on Earth. The colonised galaxy is divided thusly :
The ball of colonised space is separated into four wedges of space, all centred on Mars. These are known as the Quadspheres.
Each one of these are then separated again into another four quarters, as precisely as possible, known as Quadrants.
Each Quadrant is then again separated into another four quarters, known as Sectors.
Therefore, there are 64 Sectors (4 Quadspheres, each with 4 Quadrants apiece – making 16 Quadrants in total – and then each Quadrant divided 4 times, or 16 x 4, to give 64 Sectors).
Each Quadsphere is given a designation, on the old Earth points of the compass, North, East, South, West.
Each Quadrant within each Quadsphere is given the same designation, North, East, South, West.
Each Sector within each Quadsphere is given the same designation, North, East, South, West.
So, a ship setting off on a head of North-South-North, would be heading towards the Northern Quadsphere, the Southern Quadrant within that Quadsphere, and then the Northern Sector within that Quadrant, accurately naming one of the 64 Sectors. This is the heading.
Then two sets of numbers are given, in Interstellar Units, describing the distance on that heading from Mars, taking into account the direction of the starship before it jumps. By cross-referencing the two sets of numbers, you are given the precise location the starship or object is heading to.
An example would be : North-South-North-1002-2399.
Another ship looking at the departing starship, would only know the heading; North-South-North.
NB : although not relevant to Imperial Navigation, the Sectors, Quadrants and Quadspheres also have regions which cross over them, sometimes smaller than Sector and sometimes bigger, known as Segments, Marches, et al, but these are political divisions and stellar cartographic boundaries, and do not impact on the school of navigation.