The length of this 2-D vector. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
Syntax
Remarks
 In 2-D Euclidean space, the length of the vector is the square root of the sum of the two coordinates squared.