From https://groups.google.com/forum/#!searchin/scitools-iris/performance/scitools-iris/HajdRLOZZQ4/ypy1FzbxtkMJ, with code from https://gist.github.com/pelson/8256b9bab1c775348492 investigate why the performance of nearest neighbour is ~2 orders of magnitude better than linear interpolation.