From pins to computers
Chapter 1: Context and Concepts

Crime mapping has long been an integral part of the process known today as crime analysis. The New York City Police Department, for example, has traced the use of maps back to at least 1900. The traditional crime map was a jumbo representation of a jurisdiction with pins stuck in it (figure 1.1). The old pin maps were useful for showing where crimes occurred, but they had serious limitations. As they were updated, the prior crime patterns were lost. While raw data could be archived, maps could not, except perhaps by photographing them.1 The maps were static; they could not be manipulated or queried. For example, it would have been difficult to track a series of robberies that might overlap the duration (a week or month) of a pin map. Also, pin maps could be quite difficult to read when several types of crime, usually represented by pins of different colors, were mixed together. Pin maps occupied considerable wall space; Canter (1997) noted that to make a single wall map of the 610 square miles of Baltimore County, 12 maps had to be joined, covering 70 square feet. Thus pin maps had limited value—they could be used effectively but only for a short time. However, pin maps are sometimes still used today because their large scales allow patterns to be seen over an entire jurisdiction in detail. Today, "virtual" pin maps can be made on the computer, using pins or other icons as symbols (figure 1.2).

Figure 1.1

Figure 1.2

The manual approach of pin mapping gave way during the past decade or so to computer mapping-specifically, desktop computer mapping. For decades before desktop computer mapping, the process was carried out on gigantic mainframe computers using an extremely labor—intensive process. First, much labor was involved in describing the boundaries of the map with numbered coordinates on punched cards. Then came the labor of keypunching the cards, followed by a similar process of coding and keypunching to put the data on the map.

Recognizing all the work needed to produce a map on the computer, many potential cartographers2 (mapmakers) concluded that computer mapping was too labor intensive. They were right—it was a "royal pain." It was productive only if many maps were needed (making it worthwhile to prepare the base map, or boundary map, of the jurisdiction), and if the personnel necessary to do the data coding and keypunching were available. Few organizations could afford the luxury.

Since the mid-1980s, and particularly since the early 1990s, when computer processing speed increased dramatically, desktop mapping became commonplace and fast, aided and abetted by the concurrent availability of cheap color printers. What a partnership! Only a generation earlier, maps on paper (as compared with the pin maps on walls in police departments) had been drawn by hand using india ink3 and special pens, with templates for lettering. If a mistake was made, the lettering had to be scraped off the paper with a razor blade. If shading was needed, Zipatone patterns were cut to fit the area and burnished to stick. Those were the days? For character building, perhaps!

What does all this have to do with mapping crime today? A newfound access to desktop mapping means that more individuals than ever before have the task—or opportunity—to produce computer maps. Also the huge demand for maps means that most crime analysts, police officers, and others involved in mapping crime have received no formal training in mapmaking-the science called cartography. A body of accepted and useful principles and practices has evolved over the long history of mapmaking. Most cartography texts contain those principles but have no regard for the special needs of the crime analyst, police officer, manager, or community user of crime maps. The goal of this guide, therefore, is to provide a guide to cartography that is adapted to specialized needs and speaks the cartographer's language.

Maps

  • Are pictures of information about areas and places.
  • Help us visualize data.
  • Are like the proverbial pictures worth a thousand words.
  • Enable information to be seen at a glance.

This guide is not intended to stand alone, isolated from evolving developments in crime mapping. Ideally, it should be used in conjunction with other materials and approaches. In 1998, for example, a group working with the support of the Crime Mapping Research Center (CMRC) at the National Institute of Justice developed a national curriculum for crime mapping. Much information contained in this guide can be found fleshed out in the curriculum and other materials disseminated by CMRC. Readers are strongly encouraged to visit the CMRC Web site at http://www.ojp.usdoj.gov/nij/maps/.

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