• Introduction
• The Utility of Maps
  • Principles of Data
  • Meta-Data
  • Idea
  • Means
  • Methods
• Producing Displays
• Point Symbolization
• Line Symbolization
• Choropleth Symbolization
• Graduated Symbol
• Grid Symbolization
• Dot Density Symbolization
• Isopleth Symbolization
• Thematic Mapping
• References
• Index
• Author Index
• Symbol Index
• Site Map

The Idea of Visual Communication

The effective communication of environmental data and uncertainty as meta-data requires an understanding of the principles of visual communication and map design. David DiBiase (1990) has developed a model of information display, in a research setting, as a means of communication in a continuum from communication to self through communication to others (see Figure 1.6). Communication to self can be thought of as "visual thinking", and includes data exploration, hypothesis generation and confirmation. At this level of data visualization, maps and other graphics are used to "prompt insight, reveal patterns in data, and highlight anomalies" (MacEachren 1992, 1). The goal in the creation of these images should be to assist these goals. Because of these goals, it is with this type of visual communication that the possibility of visualization error is greatest. MacEachren and Ganter (1990) describe these errors as seeing wrong (similar to the type I error in hypothesis testing--identifying a pattern that is not there) and not seeing (similar to the type II error--not identifying a pattern that is there). But, since these graphics are generally rough and intended only for viewing by the researcher(s), searching for one 'optimal' display is less important; more views on the same data may be more helpful and reduce the chances of not seeing or seeing wrong.

Figure 1.6 DiBiase's (1990) model of the function of graphics in research. Visualization begins with exploring an idea. The idea then moves through confirmation and synthesis in a larger group of both ideas and people, and ends eith presentation (although each stage can spawn new ideas).

Communication to others can be thought of as "visual communication" and is the realm of presentation graphics. At this level of data visualization, maps and other graphics are used to synthesize data into an "abstract statement concerning patterns and relationships" (MacEachren 1992, 6) and finally to present the information to others to persuade them of the accuracy of the data assessment (MacEachren 1992, 7). Edward Tufte's (1983, 77) principles of graphic excellence can help ensure the most information is presented in a minimum of space, and that this information is conveyed ethically:

• The representation of numbers, as physically measured on the surface of the graphic itself, should be directly proportional to the numerical quantities represented.
• Clear, detailed, and thorough labeling should be used to defeat graphical distortion and ambiguity. Write out explanations of the data on the graphic itself. Label important events in the data.
• Show data variation, not design variation.
• In time-series displays of money, deflated and standardized units of monetary measurement are nearly always better than nominal units.
• The number of information-carrying (variable) dimensions depicted should not exceed the number of dimensions in the data.
• Graphics must not quote data out of context.

Tufte also discusses the concept of data-carrying ink--that is, don't put more ink on the page than is necessary to convey the information. These principles are similar to those that Morgan and Henrion (1990) propose for designing graphics for the presentation of uncertainty information. Judy Olson (1981) also suggests the need for clear and accurate legends in her guidelines for the production of bivariate maps.

Monmonier and Johnson (1990, 77) have proposed a guideline for the communication of environmental risk, which can aid in the making of maps for visual communication. Their multistep process is not a waterfall type model (when one level is completed it cannot be returned to), but rather a guideline for iterative refinement for the presentation of data. The steps they include are: setting up the design team; identifying the communication goal; the issue profile; the audience; the messages of environmental maps; methods; and evaluation. Setting up the design team acknowledges that one person may not have all of the knowledge necessary to adequately design a graphic, and that, as necessary, each of the following steps should involve each person who has or can contribute to the map. Identifying the communication goal is simply that a focus should be selected for the map; this will facilitate inclusion of important information and removal of extraneous data. The issue profile deals with the history of the problem to be mapped and the constraints on producing the map; that is, the 'environment' of the map and map design process.

The audience must also be considered when designing a graphic. This includes consideration of who will be viewing the map (politicians, scientists, the public, etc.). These different audiences will generally have varying degrees of map-interpretation skills; this influences the amount of explanatory information that should be included, the appropriateness of bi- or multivariate maps, and the appropriateness of 'eye catchers' such as bright colors. Consideration of the audience should also include an acknowledgment of how the map will be presented; this is part of the issue profile and influences the choices of methods.

Monmonier and Johnson (1990) present a list of several categories of messages that environmental maps generally present. The first of these is "What we found/What we know/What we think we know" (p12). This is the presentation of information at its most basic level, but even at this level meta-data can be presented--'what we think we know.' The second of these messages is "What you can do/What you should do" (p13). This is very dependent on the choice of audience--a lawmaker's set of choices of what to do can be quite distant from a concerned citizen's, for example. The third message is "What we're doing/What we want to do" (p13). For this type of message Monmonier and Johnson suggest that an overview map with several smaller maps of detail maps may aid the presentation. The last category is "Why we're doing what we're doing/Why you should do what we're asking you to do" (p13). This type of map should present the reasoning behind a choice or plan of action; this can include the presentation of the history side of the issue profile.

The final two steps of Monmonier and Johnson's strategy are methods and evaluation. Methods need to address questions such as the need for one or several maps, how these maps will be presented (large size color maps, 8.5x11 black and white maps, slides, video, etc.) and whether or not additional information such as non-map graphics should be included. Although evaluation is presented as the last step in map design, it is a part of each of the earlier steps. It is the last step as a review of the, possible, final design. Evaluation can be formal (a survey) or informal (a telephone call to someone who has seen the map and can suggest any possible improvements).