I came across a (brief) article in Dwell about this guy that documents these paths in the Netherlands. I remember talking about these in Architecture School (at one time I actually thought I had the smarts for this degree). They are the natural paths that people make. A great example of these is on a college campus when it snows a bunch. Before the plows plow the side walks people start making patterns in the snow. The easiest or most natural way to get somewhere reveals itself. Such an interesting idea.
Well all of these years later I come across this article of a guy archiving them. It's real hard to read (meaning impossible) because it's in dutch, but you can see a few more of these images here.