I have found some unexpected behavior of ArcGIS union tool. My assumption was that this tool will never add any new vertex to the output layer, but this was not the case.
I have run the ArcGIS union tool on only one layer GADM (world admn01) and found that in output layer there are around 866 new vertices. I think this tool make tiles of data and then process. After processing there are extra vertices which are basically created because of tiles are not completely deleted.
Is there anybody else with the same problem/experience?
I am using ArcGIS 10.0 on Windows7 64bit