Usually when I read about AdS/CFT complementarity as a particular case of the Holographic principle, it suggests that physics evolution on a boundary has a map to physics evolution on the bulk.
But what of sort of boundaries does this apply? I've usually seen it applied where the event horizon is the boundary and the outside space is the bulk. But does it hold for imaginary boundaries as well, like the typical Gaussian surfaces one consider to study Maxwell equations as well? If not, what special properties needs to satisfy the boundary so that the holographic principle holds?