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