Some friends and I were chatting about this last night while watching the heinous MacGuffins and Deus ex Machina moments in the final episode of Atlantis, oddly enough, backpedalling furiously trying to come up with alternative excuses for the coordinate system.
Our best stab was handwaving frantically and uttering something about a Hilbert curve [1][2].
But that still doesn't really explain anything about why the ancients would pull the equivalent of going from IPv6 to v4 by dropping the number of coordinates in the Milky Way gates.... or, anything else, really.
