All of the streets in the lower 48 United States: an image of 26 million individual road segments. 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. This began as an example I created for a student in the fall of 2006, and I just recently got a chance to document it properly.
This is just spectacularly awesome looking. So impressed. Art from data.