The best way to begin a discussion about maps is to define what a map is and what it does. A map is a way of cataloging information with a relational property; it is an interpretive explanation of spatial relationships. It need not represent Earth, and it need not even be real. Some of the most interesting maps chart places that don’t even exist. There are as many kinds of maps as there are things to show on a map. They can show politics, geography, topography, statistics, regions, cultures, places, transportation, demographics, history, and more. The one common feature of them all is that they show, in some way, space; whatever else they do or do not display, they show something that is physically related to other things.