Why Impedance is plotted as R + jX, with resistance on the horizontal (real) axis and reactance on the vertical (imaginary) axis. A pure resistance has X = 0, so the point has no vertical component and lands somewhere along the horizontal axis (to the right of the origin for a positive resistance).
Watch out The vertical axis is where a pure reactance plots, inductive above the origin and capacitive below; a 45 degree line would mean the resistance and reactance are equal in magnitude, not that reactance is zero.
R is Real, and the real axis runs across: pure resistance sits on the horizontal line, zero j.