The Revit API namespaces have been changed to be more consistent and more suitable to expansion. In previous releases, API classes were split along the lines of functionality and Revit vertical product, which led to confusion about where classes which were Elements or Symbols belonged if they were specific to one vertical. In the new namespace structure, there is a primary division into three sets of namespaces:

• Autodesk.Revit.ApplicationServices – contains classes accessing settings and options for the main Revit application
• Autodesk.Revit.DB – contains classes accessing data from the Revit file
• Autodesk.Revit.UI – contains classes accessing or customizing the Revit user interface

Within these main namespaces there are subdivisions based on discipline, e.g.:

• Autodesk.Revit.DB.Architecture
• Autodesk.Revit.DB.Structure
• Autodesk.Revit.DB.Mechanical
• Autodesk.Revit.DB.Electrical
• Autodesk.Revit.DB.Plumbing

Classes which are useful in more than one discipline are placed in the Autodesk.Revit.DB main namespace.

Less commonly used classes, like event arguments, are also placed in subordinate namespaces, e.g.:

• Autodesk.Revit.DB.Events
• Autodesk.Revit.UI.Events

As a result of the rearrangement of the namespaces, a few classes have been modified more drastically than simply being moved to new namespaces:

• Autodesk.Revit.Geometry.Element has been renamed to Autodesk.Revit.DB.GeometryElement to avoid a naming conflict.
• Autodesk.Revit.Geometry.Instance has been renamed to Autodesk.Revit.DB.GeometryInstance to avoid a naming conflict.
• Autodesk.Revit.Structural.Enums.Material has been renamed to Autodesk.Revit.DB.MaterialType to avoid a naming conflict.
• Autodesk.Revit.Options.Application has been removed. The properties accessible from this class have been moved into Autodesk.Revit.ApplicationServices.Application.

To obtain a full list mapping the changes from the Revit 2010 API, see the document Revit 2011 API Namespace Remapping.xlsx in the Software Development Kit install.