one can rotate the 3D without affecting the 2D.

So, understanding that the x-axis represents left and right, and the y-axis represents up and down, and that the zero on the layout is just a non-essential starting point, it appears that the missing component is the direction one is facing relative to the drawing

Does the x-axis need to be viewed from inside or outside? In other words, is the user facing a wall from inside so as to view the left and right directions, or facing it from the outside?