Working with design models, you can create one or more discrete models, simply, within a single DGN file. Using the Model tab of the Project Explorer dialog, you can quickly switch between the various models in the DGN file.

A drawing model is the intermediate between the 3D design model and a printable sheet model. It is an unbounded white space that contains one or more views of the design model. You can use a drawing model for centralizing annotations that need to be shared across multiple sheets. If you want to extend a saved view by adding annotations, dimensions, callouts, and other embellishments, create a drawing model for it. When a drawing model is attached to a sheet, the drawing model's annotation scale is used as the attachment's default detail scale.

When you first open a DGN file, it has a default design model ready to place elements. When you open the Model tab of the Project Explorer dialog, the default model has the name Default, with the Description as Master Model. You can use this model and, if necessary, change its name and description to more appropriate values.