When vehicles travel offroad, over any type of terrain such as grass, wheat, corn, etc, they leave a nice trail that is easy to spot from the air no matter how well they were camouflaged. Before, during and after Overlord the TAC fighters would follow the tracks into the woods (limiting terrain) to bomb those suspected vehicle parks, not very accurate but did enough damage that the Germans would sweep their tracks leading into the woods to hide from the Jabos. Same goes for travel in the desert, unless the ground is really hard you can follow the tracks to the vehicle.
"Don't let the dirt and rust hang you up, we like to give the impression that we are out of action badly in need of rest and reorganization"
