Maps are typically graphical representations of geography, but can be generalized to topological studies of many systems – spatial or otherwise. For example, there is The Internet Map created by Ruslan Enikeev, who describes it as:
…a scheme displaying objects’ relative position; but unlike real maps (e.g. the map of the Earth) or virtual maps (e.g. the map of Mordor), the objects shown on it are not aligned on a surface. Mathematically speaking, The Internet map is a bi-dimensional presentation of links between websites on the Internet. Every site is a circle on the map, and its size is determined by website traffic, the larger the amount of traffic, the bigger the circle. Users’ switching between websites forms links, and the stronger the link, the closer the websites tend to arrange themselves to each other.
Another example is Simon Raper’s graph of the history of philosophy, based on a data pull from Wikipedia. And there’s also the Map of Science, a series of “maps” showing the relationships between scientific studies, journals, and gaps in competence.
My thanks to Fernanda for the tip!