Compressing a DGN file reduces its size and clears the undo buffer.
The COMPRESS DESIGN key-in is used to compress files. This key-in automatically minimizes the number of levels that are in the level name dictionary (a list of all levels used in references, including nested references, in the master file). It also trims down the size of the reference attachment, view group, and saved view elements.
The COMPRESS OPTIONS <ON, OFF, RUN, TOGGLE> key-in is used to open the Compress Options dialog.
If you need to improve the performance of a DGN file, use the COMPRESS DESIGN INCLUDEREFS key-in. This key-in finds all references and nested references that are reachable from all models in the master file and compresses those files.
When you open a DGN file the product checks the size of the level name dictionaries in the file and its reference. If the number of entries in the level name dictionary exceeds the number of levels in the file by 2,000 or more, a warning appears in the Message Center. The warning tells you which DGN file contains a large level name dictionary and it advises you to use compressing. You can select OK, or run the COMPRESS DESIGN INCLUDEREFS key-in to compress the file and improve the performance. If the difference exceeds 10,000, a balloon text appears with the same warning message., turn on the Include References check box in the Compress Options dialog and click