The layers you have selected contain both contour lines and non-contour lines (lines of non-constant elevation). You may want to go back and select fewer layers, or you can continue, but the boundary of the site may be larger than you want. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
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