The catch is "corner crossing" -- stepping diagonally OVER the property boundary from public land to public land, avoiding the ajoining private parcels. However, it's legally ambiguous in some areas whether you are violating the "air rights" of the private lands as your foot glides over them without ever actually setting foot on the dirt.
In Norway this would all be obviated by the "right to roam" law that states that anyone may move freely through privately owned land so long as:
- It is uncultivated
- You don't leave any mess/trash
- You don't stay more than one night if you camp