I'm not sure why, but I could never really picture & grasp this concept. Say you're drawing the orbitals of an atom, the 1s & 2s orbitals are pretty easy to draw. They are just spheres with a node in between them. Now do these orbitals overlap, or does one start where the node ends? What really got me to ask the question is, I've got no idea about the 2p orbital, because all the pictures in the textbook show it starting at origin in the xyz plane.