GaN-based optoelectronic devices operate with defect densities orders of magnitude higher than are tolerable in other III-V semiconductors, so it is important to understand the impact of these nanoscale defects on the material's properties. There is a limit to the information that can be obtained by examining nanoscale features with a single technique. In my PhD work at the Cambridge Centre for Gallium Nitride, I aimed to directly correlate structural, optical and electrical measurements of the same specific nanoscale features. The use of novel sample preparation methods and markers to allow the same area to be investigated by a number of different sequential microscopy techniques yielded a more comprehensive understanding of the impact of particular nanostructures and defects in the nitrides.