Depends who makes the simulator - and normally I suspect it's their own visuals, tailored to the users requirements. For example most users may need less than a dozen airfield models. Airliner sims will be viewing the ground from 35000 ft. Military sims may only need a relatively small detailed area. As for flight models - as VB says, they are tailor made - remember these panels have to be fully functional and systems behave exactly as they would in the real aircraft, including such complex parts as flight engineers panels on older aircraft.
Here are a few of the manufacturers:
ThalesFrascaCAEThere are others, but I've been up 20 hours (and crossed the atlantic during said hours!) so the brain isn't functioning too well!