The next generation of FlightGear scenery (World Scenery 3.0) is currently in development. You can find regional "test" downloads on the FlightGear forums that offer significantly higher mesh resolution. 🌟 Project 2: Custom OSM Scenery
Explaining how to install for your favorite city. Which part of the world are you planning to fly in first? flightgear map download
If you prefer to fly offline or want to download specific countries/continents ahead of time, the official website provides a graphical interface for tile selection. The next generation of FlightGear scenery (World Scenery 3