(Today is Ben Fry day on kottke.org. Apparently.) All Streets is a map of the US with all 26 million roads displayed on it. The best part is that features like mountains and rivers emerge naturally from the road system.
No other features (such as outlines or geographic features) have been added to this image, however they emerge as roads avoid mountains, and sparse areas convey low population. The pace of progress is seen in the midwest where suburban areas are punctuated by square blocks of area that are still farm land.
Here are a few technical details of how the map was made.