OPG is a ZIP archive file associated with Offline Plan Generator software tool. OPG archives store XML files created by the application. Users can create such archive at any time and restore its content if needed.

Offline Plan Generator is a tool for creating diagrams and ground plans without having access to a database. The project is no longer actively developed and OPG format is considered obsolete. OPG files were mainly used in geodesy. Offline Plan Generator was developed by Landoline company.