The phrase "familiar territory" refers to a situation or place that someone knows well and is comfortable with. It means being in an environment or situation that is familiar or easily understood. Full definition
Some dogs only feel comfortable going to the bathroom in familiar territory at home. (progressive.com)
Well, that's less familiar territory for most people. (social.hays.com)
In establishing the policy on licensed personal assistants, we found a more familiar territory with the caveat that the licensed assistant is under the control of both the principal salesperson and the broker. (realtormag.realtor.org)