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Update Polygon Geometry

Question asked by kafros on Nov 4, 2013
I have a feature class of large polygons (Projects) that should encompass and line up with the boundaries of a serious of smaller polygons (Parcels).  Somehow the projection of the Parcels has skewed over the years so that some of the Projects do not line up -- see Poly1.gif attached. 

In other places in my feature class, the Projects DO line up with groups of Parcels.  I need to get everything to line up.  Since I don't know the original projection(s) and some Projects are only a little skewed, some a lot and some not at all, I can't easily do a Transformation or Georeferencing and still ensure everything lines up properly. 

What I was thinking is that I could create a batch editing job using ModelBuilder or Python script, but I need some help.  My thought was to loop through each Project (over 3000!) and for each of those polygons:

1.  Select the Parcels (green outline) that have their centroid inside of the Project (maroon cross-hair selection) -- see Poly2.gif attached.

2.  Clip the Project polygon to match the selected parcels -- see Poly3.gif attached.

3.  Merge the shape of the selected Parcels with the clipped Project to update that row in my Projects feature class.  -- see Poly4.gif attached.  Note: Projects CAN be multi-part features. 

This should get me close enough for most of the projects.  Some will have to be manually updated if Parcel centroids don't land in the right Project, but I'm thinking this will fix the majority of Projects.  The big problem I'm finding is that I want to update the existing Project feature class and each of it's features within it.  Using Clip, Merge, Union creates new feature classes.  If I manually edit each Project polygon I can update the existing feature and retain the original ObjectIDs, but this is too time-consuming.  Can anyone assist me with a script or model tool that won't require creating new feature classes to get my Project polygons lined up?

Thank you.