Two-dimensional thinking in space navigation has a venerable tradition. The classic science fiction RPG Traveller famously and unashamedly uses a two-dimensional star map, completely ignoring the third dimension in the relationships between stars. This was later justified in that the star maps represent navigable hyperspace "jump routes", with hyper-distances between stars happening to fall into a two-dimensional geometry that only partly reflects the real three-dimensional relationships between them. Essentially the hyper-distance between stars is measured along a projection of the real-space route onto the Galactic plane.

The one big advantage of this convention is that you can easily draw a map on a sheet of paper, rather than needing a rotating 3D model or some sort of holographic display.

And, as Captan Kirk once showed to his advantage, even geniuses sometimes forget that space has an up and a down.

Transcript

Han: Turn right!
Leia: Go left!
Chewbacca: Space is three-dimensional. I go down.
GM: Asteroids are flying in all directions. Make a Pilot check.
Chewbacca: With ease, old chap. 12.
Leia: I hate to say this, but I wish we had some idiot genius vector-calculating savant here.
Han: I'm some of those things!
C-3PO: I can calculate vectors! I use the left hand rule!
Leia: What's that?
C-3PO: Go the way my left hand points, silly.