How crime maps do what they do
Chapter 2: What Crime Maps Do and How They Do It

A detailed discussion of how maps communicate through processes of visual comprehension is beyond the scope of this guide. However, a few points are made here to explain the underlying process and underscore the idea that people see maps differently due to differences in, for example, their eyesight, aptitude for visual comprehension, and prior training. A background problem that goes largely unrecognized in the community of mapmakers is that, for some people, maps have no meaning. They may grasp neither scale nor symbolization. As a result, they have no sense of distance, relative or absolute, and are unable to draw meaningful conclusions from a map.

This problem is, in part, a legacy of the disappearance (until recently) of geography from school curriculums. But it may go deeper, seemingly having to do with gender- and race-specific differences in personal mobility that, in turn, may hinder the development of spatial experience and reduce individuals' abilities to take advantage of maps as tools. For example, in the past, women's traditional roles in childrearing have limited their mobility, thus denying them opportunities to learn geography by directly experiencing places. Race has had a similar indirect effect through the mechanisms of discrimination and depressed economic status. Insofar as minority groups have experienced disproportionate levels of poverty, their mobility has been limited and their geographic learning correspondingly stunted. (See Montello et al., 1999, for a discussion of related questions.) While the police are very geographically aware, in part due to much field experience, individual members of the community may not be. An argument might be made for giving special attention to maps intended for the community. For example, digital photos of landmarks could be embedded in a community map as visual anchors to show residents how the map relates to their environment.

All messages, including maps, are laced with nuance. "The medium is the massage," wrote McLuhan and Fiore (1967), arguing that literate people had been rendered visually incompetent by an excessive dependence on text. Since that famous remark, personal computers have provided an interactive platform, allowing what is, in effect, environmental manipulation on the fly. Maps, text, and data have moved from the realm of the passive to the active and interactive, encouraging perception of the map as a tool rather than as a mere display device.

Peterson (1995) has outlined several theories and models that have been advanced to explain how visual information is processed:

  • Stage model. Visual information moves through three memory stages. The first (iconic) is very short and deals with initial recognition. The second (short-term visual store) is longer but has less capacity so complexity becomes an issue. Moving from iconic to short-term demands attention. The information is then sent to long-term visual memory. Long-term images provide cues to help with recognition of new visual stimuli.

  • Pattern recognition theory. Iconic images are converted into something recognizable through pattern matching.

  • Computational model. This sophisticated three-dimensional model is similar to the process of abstraction in cartography. (For additional discussion, see Peterson, 1995, chapter 1.)

These theoretical considerations are reminders that producing a map is only half the story. We also have to be concerned with how it is interpreted by the intended audience. The storage of cues for the interpretation of visual images in long-term memory means that familiarity provides a substantial advantage in the interpretation of maps. We may be oblivious to the fact that our map is extremely familiar to us but means little or nothing to those who have no reference points in their long-term memory or who have had insufficient time to study and process the details.

Another way of visualizing the process of moving a concept from the analyst to the map user is illustrated in figure 2.2, showing that the cartographer's and map user's realities are both abstractions of reality. The cartographer creates a cartographic abstraction and translates this into a map that is read by the map user and transferred to the user's mind.

Figure 2.2

Chapter 2: What Crime Maps Do and How They Do It
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Mapping Crime: Principle and Practice, by Keith Harries, Ph.D., December 1999