[ccernaf]

Maps are just visualizations that focus on one attribute almost everything has: a spatial location. They don't need to show rivers or other physical features. A map of voting patterns for instance doesn't really have physical features. If you distort it to reflect population, you have an even looser map whose only tie to the world is the relative location of one area to another.

Physical maps like those that the USGS provide are just a tiny sample of the breadth of maps out there in the world. There are many, many really cool, non-traditional maps out there.