This is 1A, there is 50ft of hallway without doors that slopes up gently, then down severely, to the left, which is the way you went.
This is 1B as you've seen it so far, note that the scale (like the hallway's construction) is not the same. (here a square is 10ft) the numbers written in correspond roughly to the depth below sea level (bigger #=deeper) The area I've marked in black is where the necromancer-using her advanced math skills-is pretty sure you're UNDER the above hallway and perpendicular to it.
Don't read anything into the scanner artifacts in the left hand corner. there is not a secret room THERE. (or on this part of the map)