We can work with tracks in 2 or 3 dimensions. The difference between them is that, as well as the usual details on coordinates, time and date, a 3 dimensional track also includes details on the altitude of each track point.
Land/Air’s 3D viewing window allows you to view both types of tracks but a 2D track will have a flat appearance or, if you have loaded a landscape, it will appear glued to the landscape.