The Topic Maps Reference Model (TMRM) defines the qualities of subject mapping that distinguish it from other information technologies. It defines subject maps very abstractly in order to avoid limiting the design choices that can be made when creating them. However, its high level of abstraction is not helpful to readers who need only to grasp its essential principles. Using commonplace examples, this paper illustrates those principles. Briefly, they are that authors can determine what subjects they wish to represent in a subject map, how information about those subjects is expressed, and how, when two or more representatives represent the same subject, they should be viewed as a single representative. The TMRM provides requirements that disclosures of such design choices must meet in order to facilitate the interchange and exploitation of subject maps.