Civitas-G was a moon in orbit around Civitas. Prior to Bernice Summerfield's time, the people of Civitas colonised the wasteland which was Civitas-G. Bernice Summerfield did a dissertation on this period of their history while she was at university.
Some time later, the people of Civitas-G moved towards spending their entire life in a virtual reality. This lasted until the man who later became known as the Administrator, gained the power to manipulate the artificial reality, and began reshaping the world, and its history, in order to put himself in control.
When Bernice Summerfield, the Doctor from a parallel universe showed up, they eventually found out about the Administrator and his deeds, and helped a citizen, Zita, to topple the regime. (AUDIO: Clear History)