Anyone can play in the mode of their choice and switch between the two whenever they want via the settings page.
EDIT: Also worth noting:
- The 'Map' mode in 3D is there to provide an overview while in 3D mode. It is not a replacement for the 2D viewer, which was another common misunderstanding.
- Old versions of the 2D app will not display races correctly. Cars will warp all over the place and drive at the wrong speeds. You must be on the latest version of the app for 2D to work correctly. We've also seen some reviews still on old versions of the app (3.xx) trying to use this to play in 2D. This is not a solution. The proper solution is to get the latest version and switch to 2D mode if that is what you want.