An electromagnetic wave is typically shown with this schematic (taken from https://en.wikipedia.org/wiki/Electromagnetic_radiation )

We see graphically from the schematic that the amplitude of E and B is is evolving with position and time.

Thus, should we consider that the electromagnetic wave has a lateral extension ?

Or is there no lateral extension : that is meaning that we should consider the electromagnetic wave as a pure mathematic line (not as shown in the schematic) where the electric field have a different value depending on the position on this propagation line ?