A　correlation　study　between　the　observed　surface　morphology　using　high-resolution　scanning　electron　microscopy　(HRSEM)　and　the　observed　structural　imperfections　using　transmission　electron　microscopy　(TEM)　has　been　conducted　for　a-plane　GaN.　There　are　three　different　sized　asymmetric　surface　pits:　large　pit　of　500　nm-2　A　mu　m　in　side　length,　medium　pit　of　50　nm　in　side　length,　and　small　pit　with　side　lengths　of　less　than　5　nm,　which　originate　from　incomplete　island　coalescence,　screw　dislocation,　and　partial　dislocation　(PD),　respectively.　Both　screw　dislocation　and　PD　can　produce　pits　on　the　free　surface　because　they　have　a　perpendicular　line　tension　to　the　surface,　which　must　remain　in　balance　with　the　surface　tension.　The　two　types　of　dislocation　lead　to　distinctive　pit　sizes　because　the　PD　has　a　smaller　Burgers　vector　component　along　the　dislocation　line　than　the　pure　screw　dislocation.　A　pit　that　is　produced　in　the　island-coalescing　process　is　much　larger　than　those　caused　by　dislocations　because　island　coalescence　is　a　kinetic　process　that　involves　large-scale　mass　transportation,　whereas　the　dislocation　mediates　the　surface　in　the　local　area.　These　three　types　of　surface　pits　sometimes　interact　with　one　another　in　space.　The　coalescence　of　the　island　determines　the　surface　morphology　at　large　scales,　whereas　the　defects　affect　the　details.