  Hole-ography is a prescription relating the areas of surfaces in an AdS bulk
to the differential entropy of a family of intervals in the dual CFT. In (2+1)
bulk dimensions, or in higher dimensions when the bulk features a sufficient
degree of symmetry, we prove that there are surfaces in the bulk that cannot be
completely reconstructed using known hole-ographic approaches, even if extremal
surfaces reach them. Such surfaces lie in easily identifiable regions: the
interiors of holographic screens. These screens admit a holographic
interpretation in terms of the Bousso bound. We speculate that this
incompleteness of the reconstruction is a form of coarse-graining, with the
missing information associated to the holographic screen. We comment on
perturbative quantum extensions of our classical results.
