Suppose my reference system is x coming out of the page toward you, y is in the plane of the page going left and right and z is in the plane of the page going up and down. Further suppose that the magnetic field is parallel to the x axis and the electric field is parallel to the z axis. Finally, assume the direction of propagation of the electric and magnetic fields is along the positive y axis, as would appear to be dictated by the Poynting Vector, E X B. If I now wanted to represent the magnetic vector potential (from which the B field is generated) on a diagram as described above, how would I draw it? Is it parallel to the z axis or parallel to the y axis or would it be at some other arbitrary direction? I am not sure I am even asking the right question yet but I am struggling to visualize the magnetic vector potential with respect to the propagating electric and magnetic fields. Thanks in advance.