Rules as Written. (It's the holy grail of the rules lawyer and the lingo appeared around the same time as D&D 3.0 I believe.)

Anyway, there are two types of campaigns out there, AoR and EotE. Either benefits from the ability to plot routes that are not known to the general public and/or the Empire. It does not always have to be fight or flight, maybe you just want to make sure you avoid attention. Think of it as the Stealth skill for Starships - in the sense that you're looking for backdoors.

2D is reasonable for representing interstellar distance relationships. Most star systems will be in the galactic plane. Could you go up and over (or under)? Technically yes. But Star Wars does some hand waving to suggest why it doesn't happen. Apparently moving too far away from the galactic plane is difficult for hyperdrives to do. No idea why, just is. The fleet rendezvous at the end of Empire Strikes Back was as high above the galactic plane as they could get the ships to go, which is why "nobody would look there."

For a planetary system, 3D is much more achievable, but all your destinations will be in a single plane anyway so at least for a map, 2D makes sense.

I would think Star Wars computers could handle 3D calculations, but perhaps plotting a hyperspace or even interplanetary course takes a lot of calculation power, and 3D variants would take even more. Thus, another use for Astrogation:

"You want to override the nav-computer and plot a non-standard route? Sure. Astrogation roll please..."

Good. Thanks for the discussion. I have got some ideas on what to do with Astrogration.

Although, I have to say I am with Maelora here. If it would have been my chooice, I would have kept Surveillance and ditch Astrogration, including it into Computers.

3d stuff is important, and the essential atlas deals with it on some level. However in relative terms the Galaxy is nearly "flat" on a large scale. When the Milky Way is 100 to 120 thousand light years across, but only 2000 light years thick, the Z axis wouldn't really come into play until you get into a sector.