The Root of the Behavior
Dog walkers and trainers have all observed patterns of behavior in dogs that can lead to him making paths in the yard, regardless of where he makes the path. One theory pulls from his wolf ancestry. Wolves apparently only use trails and paths when navigating their territory. Rather than blazing a new territory, they conserve energy by staying on the tried and true path. When your dog makes a path, it is most likely the shortest point between his entrance to the yard and his preferred area of the yard. In the wild, wolves mark their paths with their scents so that they can always find their way back should they lose the pack or get confused. Your dog may simply be tapping into that instinct.
Another theory regarding path making in your pup relies more on the doggy see-doggy do theory. When you walk your dog, you tend to walk along the sidewalk and keep him walking beside you as part of the training. He also observes you walking and you also most likely keep your walk line the shortest distance between two points. Whether this behavior shapes his behavior or adds to his wolf instinct of preserving energy is not clear, but it has been noted by trainers and researchers that you can be unintentionally training your dog to create and stay on a path as often as possible. In the same vein of training your dog, he does like to have boundaries. Knowing what is expected of him limits his anxiety. Staying on a path with you while walking is clearly what you want from him, so perhaps he repeats that in the lawn to be obedient.