Why is this information not shown on maps sent to the parents of students, or to people who purchase tickets for sports, fine arts, conferences, etc.? Because for these map readers, the mapmakers are not interested in providing reassurance about the safety of the campus -- if the map contained explicit references to safety zones, there are also implicitly danger zones.
Following this exercise, I try to get students to broaden the idea of mapping by discussing the functions of maps as they relate to other forms of communication. Computer user manuals, for example, are maps of software and hardware, encouraging one method of communication over others (and often one particular method of textual production). Computer interfaces themselves, as people like Cindy and Dickie Selfe have argued, are maps of corporate relations. The desktop metaphor, for example, validates the traditional, corporate environment, but there are many others (something Microsoft, among others, has recognized). And research reports created by business and technical communicators are maps of research, highlighting aspects considered important by the writers and subordinating others.
Where conventional ideas about the value of communication placed emphasis on the original thinker of an idea (a problematic concept for professional communicators, who get much of their material from others), a postmodernist model of communication prioritizes (or at least makes visible) the value of arrangement.