Mapping as a special case of data visualization
Chapter 1: Context and Concepts

Desktop computing has put graphic tools within the reach of virtually everyone. Preparing a publication-quality graphic, statistical or otherwise, was an arduous process a generation ago. Today it is much easier, although the process still demands considerable care and effort. This new ease and flexibility have broadened our perspective on graphics as tools for the visualization of information. This has happened because people no longer have to devote themselves to one specialized, time-consuming methodology, such as cartography. Now, maps can be produced more easily, and the computer has in effect freed people to produce other kinds of graphics as needed, such as bar charts, scatter diagrams, and pie charts.

The downside to such ease of production is that it is just as easy to produce trash as it is to create technical and artistic perfection. Famous graphics authority Tufte (1983, chapter 5) referred to what he called "non-data-ink," "redundant-data-ink," and "graphical paraphernalia"—all summed up by the term "chartjunk," a concept equally applicable to maps and charts. An exemplary map, according to Tufte, was prepared by Joseph Minard in 1861 to depict the decline of Napoleon's army in Russia in 1812-13 (figure 1.5). Tufte noted that "it may well be the best statistical graphic ever drawn" (Tufte, 1983, p. 40). What makes it so good is that it shows six variables with extraordinary clarity and without the use of color variation. The width of the bands is proportional to the number of troops, starting with 424,000, which was reduced to 100,000 by the time they reached Moscow. The map shows attrition on the return trip (with vertical rays expressing temperatures on selected dates) that left only 10,000 men still alive when the army returned to the starting point. The fact that the map illustrates the devastating loss of life further adds to its drama.

Figure 1.5

Today's simplified graphics-producing environment helps put maps in perspective. Maps are but one way of representing information, and they are not always the most appropriate mode. If information about places is being represented, maps may be the best format. However, if no geographic (place-to-place) information is present, such as when all the data for a city are combined into one table, there is nothing to map. The whole jurisdiction is represented by one number (or several numbers, each representing the city as a whole), so the map, too, could portray only one number. In this situation, a bar chart simply showing the relative levels of each crime category would be the best choice.

What does it mean to say that maps are a form of visualization? Simply that a map is data in a form that we can see all at once. Books or tabulations of data are also visualizations in the sense that we assimilate them visually, but they are labor-intensive visualizations. Maps and other graphics are essentially pictures of information, those proverbial pictures "worth a thousand words." If they are well done, they convey their message more or less at a glance.

Chapter 1: Context and Concepts
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Mapping Crime: Principle and Practice, by Keith Harries, Ph.D., December 1999