Typography (from the Greek words τύπος (typos) = form and γραφή (graphe) = writing) is the art and technique of arranging type in order to make language visible. Typography maps depict geographic features that are usually represented by point, lines and polygons using type. For example, a road will be depicted in type using the road name repeated over the length of the road, while polygons are filled in with type describing the geographic object.
Paula Scher is an American graphic designer/artist that started making beautiful typography maps in the 1980’s. In 2009 she was invited to TED and gave a presentation where she talks about her maps toward the end of the video (18 minutes in). You can see her maps at better resolution here. There is also an excellent interview with her at Huffington Post where she discusses the maps.