In the building design process, remodels and additions are more common than just constructing a new building. Therefore, you will commonly have existing modeled graphical objects shown in the same view as objects that are constructed new during in the project. When this occurs in an Autodesk Revit project, you have choices on how the new and existing information is graphically represented.
There are two primary methods for showing both existing and new objects in the same view. Both methods show the same information, but show them different graphically.
Applying Technology to Architecture 