It seems to represent a galaxy code
As we see in S02E16 of Stargate: SG-1, "The Fifth Race":
SIMMONS: Wormhole is tracking… (freaked out, then to Carter) Captain?
CARTER: Sir, the computer indicates that the wormhole is leaving our
known network of Stargates. It's going outside of our galaxy. Far out.
[O'Neill continues to gaze out at the Stargate.]
DANIEL: That's why the Gate needed all the extra power.
on, I thought Stargate addresses were six points in space with the
seventh being the point of origin.
CARTER The extra chevron must add a
new distance calculation to the existing points. It's kind of like
dialing a different area code.
The same sort of thing might be at play here. From Stargate: Atlantis, S01E01:
WEIR: The point of origin, Earth.
JACKSON: That's not it.
McKAY: Then your address must be incorrect.
JACKSON: Not incorrect… incomplete.
(He draws another symbol in between the sixth symbol and the Earth
WEIR: What are you saying, Doctor Jackson?
(Daniel numbers the newest symbol 7 and the Earth symbol 8.)
JACKSON: It's an eight symbol address. What we're looking for may be
further away than we ever imagined, but it's not out of reach.
How was this code determined?
I don't think there's any canon evidence, but we can probably rule out two possibilities.
- To add meaningful information, the galaxy code has to be something that can't be determined from the other six symbols, so I don't think they could have calculated it that way.
- It certainly cannot be the same address that reaches the Ida galaxy. Again, the identifier should be unique; otherwise why have a galaxy code at all?