CYOAGOU HA-Y d1-
30
Region name: This narrows the location down to a 1280x1280x1280 cube - the Cyoagou region. The galaxy fits inside a 64x64x6 region box, many of which are entirely empty.
Subregion code: Depending on the masscode, this narrows the location down to a smaller cube (10x10x10, 20x20x20, 40x40x40, etc) - in this case, the "HA-Y 1" region. Technically the mass-code is part of the subregion code, but the mass-code is sufficiently useful that it's considered separately.
Mass-code: This is based on the amount of mass in the system. "d" is a medium-mass dwarf star with ~1 Sol mass or slightly bigger.
Serial number: Gives each system a unique name. So this is the 31st (it starts at zero) "d" mass system in HA-Y 1.
Masscodes:
H: extremely large stars. A single 1280x1280x1280 cube covers the entire region, so these don't have subregions. O-class, Wolf-Rayets, really big black holes, supergiants, that sort of thing
G: very large stars. Subregion size 640 LY. Similar star types to H, but a bit smaller.
F: large stars. Subregion size 320 LY. Mainly very large B-class stars and the resulting black holes.
E: large main sequence stars. Subregion size 160 LY. Small B-class and large A-class stars, and the resulting neutron stars.
D: main sequence stars. Subregion size 80 LY. Large G-class, F-class or small A-class stars, or white dwarfs.
C: small main sequence stars. Subregion size 40 LY. K-class and small G-class stars.
B: red dwarfs: Subregion size 20 LY. M-class stars and some small K-class.
A: brown dwarfs: Subregion size 10 LY. Mostly brown dwarf stars, but a really small M-class occasionally can be this light.
The "a" masscode subregion names are allocated simply based on AA-A 0 being in one corner of the region, AA-B 0 being next to it, and so on throughout the cubic grid to ZZ-Z 0, which is followed by AA-A 1. The larger masscode region names work similarly. It's well understood - there are tools which will estimate a star's position based on its name - but I always get confused exactly how the numbering works for the bigger subregions so I won't try to explain that here.
You can also get named zones which are smaller than a region and don't align - for example "Col 285 Sector". These override the normal name, and have their own subregions.
And ... one final point, subregions with a 0 index have that omitted in the official name. So "HA-Y d0-16" would appear on the map as "HA-Y d16". You can search for it by either name.