OpenCities Map does not have a "shared" option that allows more than one user to be in the same file at the same time.
If you are using SQL Server Spatial or Oracle Spatial to store feature geometry, then the following information may be of value:
Normally Bentley Map users work in a non-versioned, pessimistic transaction. That means features must be locked before editing. When they are locked, they cannot be edited by other users. All changes must be posted back to the spatial database or be discarded before the end of the editing session. This is also referred to as "short transaction mode" and applies to SQL Server Spatial, Oracle Spatial and PostgreSQL.
If you're working with Oracle Spatial, you can work in a versioned, optimistic transaction mode if desired. This means that you can create a new version in Oracle in which to do your edits. Features do not have to be locked for other users to edit. Versioned changes do not have to be committed to the master or parent version if an editing session ends. However, any changes made to the version should be posted or discarded before closing the edit session. This is also referred to as "long transaction mode" and only applies to Oracle Spatial.
To work with Bentley Map in a versioned environment, Oracle’s Workspace Manager must be installed and the tables being edited must be version enabled. To perform conflict resolution using the Conflict Inspector dialog, you must have the WM_ADMIN role granted.
You still have the option of working in a pessimistic mode (short transaction mode) when selecting a version. Doing so means the features must be locked before editing.
Lastly, even if your features are stored in a spatial database, each user will still need to work in their own individual design files since you cannot have multiple users opening the same design file at the same time. To avoid locking issues, each user should work in discrete area and try to avoid overlapping areas.