What rule system are you using? The following is from CT canon. And is also at COTI under library data.
Astrography
The science of mapping interstellar space. Basic to any science of mapping is a coordinate system. The system used by the imperium is based on rings of longitude, rays of latitude, and parsecs. Rays of latitude extend from the galactic core, while concentric rings of longitude are placed at one parsec intervals. By convention, the concentric ring passing through Reference/Capital is labelled the 10,000th ring, and is used as a baseline. Similarly, the ray of latitude extending from the center of the Galaxy through Reference/Capital is designated as the first ray. Measurement is in parsecs, counting in the trailing direction. Computation reveals that the circumference of the 10,000th ring (r=10,000) is 62,832 parsecs. Counting spinward uses a subtraction from 62,833, which is the equivalent of the zero baseline.
For example, Regina, of the Regina Subsector, in the Spinward Marches, is 9930 ring/ray 62723. The format for expression of location is xxxx ring/ray yyyyy, where xxxx is the ring of longitude (distance from the galactic core in parsecs), and yyyyy is the distance of the ray of latitude (in parsecs) from the first ray of latitude, measured along the ring of longitude in the trailing direction.
This mapping system is highly lmperio-centric, and other systems are used by other peoples and races outside the imperium. This system has gained wide acceptance, however, among imperium dominated client-states, human and otherwise. This mapping system breaks down and is prone to error beyond certain limits. it does serve admirably for a band approximately 400 parsecs wide at a longitude of 10,000 parsecs.
Authority: SUPP-8
You could just adjust this for YTU or maybe have something weird. Like instead of seeing the universe as flat (as humans tend to) they might map its height or density etc.
James