Given its size, it can help to take a step back and understand how this API is generally structured. The Revit API exposes around 1700 classes, 50 interfaces and 500 enumerations which cover almost every aspect and function of the application. The classes are subdivided between several namespaces, often relating to a specific usage (e.g. plumbing or structural steel). The vast majority of classes reside in the Autodesk.Revit.DB namespace.