electric wall and magnetic wall

on what basis the Electric wall and the magnetic wall are selected in a structure?
Is that based on experience or on the field distribution on the structure before solving it ?
Declare if there is some reference based on that ...
thanks in advance

yes, it is assumed that you know how the electromagnetics will behave, or how you want to enforce them. mostly based on even/odd modes inside the system. if you know/want the electric fields to be normal to the surface, apply electric wall. or if you want magnetic fields to be normal, apply magnetic wall.

you may also search for symmetry planes.

thank you for the answer, still some misunderstanding stuff!
If I have at the same time electric and magnetic wall should they be perpendicular to each other ? and this apply only for 1 mode ?
on the other hand what you mean by symmetric wall ?
thanks in advance