  We report on wide-field optically detected magnetic resonance imaging of
nitrogen-vacancy centers (NVs) in type IIa polycrystalline diamond. These
studies reveal a heterogeneous crystalline environment that produces a varied
density of NV centers, including preferential orientation within some
individual crystal grains, but preserves long spin coherence times. Using the
native NVs as nanoscale sensors, we introduce a 3-dimensional strain imaging
technique with high sensitivity ( $< 10^{-5}$ Hz$^{-1/2}$) and
diffraction-limited resolution across a wide field of view.
