We know from experiments that topological phases exhibit spectral phenomena which survive significant geometric deformations and require no periodicity whatsoever. Thus the interesting perturbations explore regimes that go far beyond the idealized band theory. I will gently introduce coarse geometry and index theory as the mathematical core of the topological phase idea. As examples, we can rigorously analyse quantum Hall effects on strongly curved and dislocated 2D samples, and prove that anomalous gapless boundary states appear regardless of the small-scale specifics of the sample.