I know I’m weird, but I’ve always really liked the way roads combine with badly maintained trucks to create emergent topographical self-documentation. Pictures are easier:
Notice the dark spots? That particular stretch of road always drives the point home for me – every time the trucks in front of me hit a bump or dip in the road, it shakes some grease loose from their chassis, and darkens the road a little bit. Like ants finding efficient routings, it’s always just sort of made me happy.
[Note: The embedded google map got very very broken in RSS, so I’ve replaced it with a static graphic. Still I suspect the RSS damage is done.]
meandering wildly 
I enjoy trying to deduce the same sort of information from my pet hobby, namely at airports.
http://maps.google.com/maps?f=q&hl=en&geocode=&time=&date=&ttype=&q=san+francisco+international+airport&sll=39.846504,-104.682026&sspn=0.060889,0.100594&ie=UTF8&ll=37.615387,-122.375336&spn=0.031411,0.050297&t=k&z=14&om=1
You don’t need San Francisco International’s operational statistics to tell that the majority of the landings throughout the year happen on the 28s, some landings happen on the one-nine-left, and no landings occur on the 1s. I would say no one lands on the tens either, but there are published instrument approaches to those runways.
Of course, the pavement tells a different story…
There are graphs all around us, from the skid marks on runways mapping out where planes most often touch down to the trails we pad out trying to easily get from point a to b.
I was in Italy at the start of the 2000s and was visiting an 800 year old church. The main door to the church was a huge and thick slab of bronze that swung inwards into the church. There was no handle on the outside, just a smooth , gently sloping depression in the metal a bit lower than my where millions of touches (from shorter people) had each carried away a miniscule bit of the door.