This archive tracks four layers. A record present in 2 of them (M41, IND) is silent in the rest, and says so.
The Horus HeresyM30–M31
[RECORD LOST]
No record for this location in The Horus Heresy.
Age of the ImperiumM32–M40
[RECORD LOST]
No record for this location in Age of the Imperium.
The 41st Millenniumpre-Rift
imperium
Ocean world of Ultramar
Storms, archipelagos and one great sea, and a population that recruits into the Ultramarines out of all proportion to its size. The Chapter Master's own world.
Era Indomituspost-Rift
imperium
Ocean world of Ultramar
Held, and rebuilt after the daemon incursion that came up out of its water rather than down from its sky.
Position
Map frame: 704, 584 in the archive's 0–1000 disk space (core at 500, 500).
Distance from the core: 221 units ≈ 23.5k light years, south-east of the galactic core.
Height above the disk plane: -6.2 units — invented thin-disk jitter, deterministic per record. No published source gives any location a z coordinate.
System: Talassar System
Books set here
1 title in the reading tracker touches this record, 1 of them as a primary location. Titles link out to the tracker.
Every fact in this record, and where it came from. Editorial derivations say so.
segmentumhigh
wh40k.lexicanum.com/wiki/Talassar infobox Segmentum = Ultima Segmentum; Sector = Ultima Sector; https://wh40k.lexicanum.com/wiki/Planets_(List) adds 'Part of Ultramar'
classhigh
wh40k.lexicanum.com/wiki/Talassar infobox Class = 'Adeptus Astartes Homeworld, Ocean World'; https://wh40k.lexicanum.com/wiki/Planets_(List) = 'Civilised World / Ocean World'. Both published classifications agree it is an ocean world
gposmedium
derived: an Ultramar world, so placed inside the Ultramar knot this dataset already carries — beside Macragge and Calth, on the Macragge side
systemlow
wh40k.lexicanum.com/wiki/Talassar_System exists and states it 'has no known worlds', and warns explicitly that Talassar 'could potentially be located in the system... but there is no evidence that this is the case'. The systemId here is our own filing convenience, not a canon claim, and no system file is shipped for it