If you have the Repository Log activated, you can consult the History sub-tab to see changes.
Or use Repository Snapshots if your are using that.
As far as i know there is no versioning feature for a city planning area.
Option 1: You can follow the progress or changes that have been made to the city planning area by going on the object-->Right Click--> History (right click on the object) in the web client and export to excel. In the rich client (mega.exe) via the General Tab--> History of the object.
Option 2: Repository snapshot feature as stated by hsoegaard
Hope this info helps.