We present a direct microscopic correlation between local optical properties, characterized by spectrally resolved cathodoluminescence microscopy and the microscopic crystallographic orientation determined by electron backscatter diffraction at identical sample positions of nonpolar and semipolar GaN growth domains simultaneously formed during metal-organic vapor phase epitaxy on the same r-plane sapphire substrate. The luminescence from all nonpolar, (112_0) grown crystallites is dominated by the basal plane stacking fault luminescence, while all crystallites having semipolar (112_6) orientation show a luminescence characterized by pure excitonic emission, i.e., without any contribution of stacking faults, and with an order of magnitude enhanced quantum efficiency.