The GIS revolution|
Chapter 4: Mapping Crime and Geographic Information Systems
Although it is tempting to think of geographic information systems (GIS) as a thoroughly contemporary technology, its conceptual roots reach far back. A GIS is based on drawing different spatial distributions of data on paper (or other suitable media) and overlaying them on one another to find interrelated points. Foresman (1998) notes evidence that this model was used at the Angkor Wat temple complex (in today's Cambodia) in the 11th century. Modern geographic information systems can be linked to developments in the 1960s, including land use analysis in the United Kingdom by Coppock (1962), development of the Canadian GIS by Tomlinson (1967), and publication of McHarg's Design with Nature (1969).
Early GIS efforts were restricted by the limitations of older computer systems lacking memory and speed, such as the 512k memory of the IBM 360/65, a
computer widely used in the 1960s and 1970s (Tomlinson, 1998). This limited the size of data sets and made it difficult to simultaneously manipulate multiple observations or large numbers of variables.
These constraints limited the attractiveness of GIS technology to law enforcement agencies. Weisburd and McEwen (1997) noted that police departments typically lacked the computer resources and the base maps necessary to support a GIS operation. Labor, startup, and operational costs, such as coding incident addresses for the computer, were prohibitive, and the field lacked user-friendly software.
What Is a GIS?|
A GIS is a computerized mapping system that permits information layering to produce detailed descriptions of conditions and analyses of relationships among variables.
Strictly speaking, any system that permits the representation and analysis of geographic information is a geographic information system. The acronym GIS is understood to refer to computer-based software, generally in the form of a few popular proprietary software packages. Although a prominent component of a GIS, proprietary software does not define a GIS.
Even the acronym "GIS" is the subject of debate, with some arguing that "s" stands for "system(s)," while other object that this is too narrow and the "s" should stand for "science."
The earliest applications of crime mapping appeared in the mid-1960s, according to Weisburd and McEwen, who cited the work of Pauly, McEwen, and Finch (1967) and Carnaghi and McEwen (1970). Most early crime maps were produced using the SYMAP program developed at Harvard University. Input required punched cards, and output was produced on a line printer that limited detail to the size of the printer typeface. Shading of choropleth maps was accomplished by overstriking printer characters so that they darkened (figure 4.1). All maps produced this way were black and white. Line symbol mapping (of auto thefts, for example) was done on a plotter (figure 4.2). (See Weisburd and McEwen, 1997, for additional information.)
Later, the SYMVU variant of SYMAP used line renditions on a plotter to produce three-dimensional visualizations, like that shown in figure 1.13. Pioneering work done in St. Louis by the police department involved the establishment of a Resource Allocation Research Unit with the objective of improving the efficiency of patrol operations. The unit recognized that fixed boundaries would have to be established for crime mapping purposes. This was done using so-called Pauly Areas, named for (then) Sgt. Glenn A. Pauly, who designated mapping areas similar in size to census block groups. Thomas McEwen then devised a system for geocoding by relating street segments to Pauly Areas. This was the first time in an operational setting that computerized visualization of crime data was recognized as a management tool.
GIS applications in policing took off in the late 1980s and early 1990s as desktop computing became cheaper and software became more accessible and user friendly. To date, large departments have been more likely to adopt the innovation; however, almost any police agency that wants a GIS can have one. Foresman (1998, figure 1.2, p.11) recognized five ages of GIS development.
The Pioneer Age, which lasted from the mid-1950s to the early 1970s, was characterized by primitive hardware and software. The Research and Development Age lasted into the 1980s and overlapped the Implementation and Vendor Age, which in turn lasted into the 1990s, when the Client Applications Age began. The Local and Global Network Age followed.
Crime mapping came of age in the Implementation and Vendor period, when computing costs began to fall and software became more immediately useful. Over the past decade we have also seen more examples of police departments commissioning customized versions of software to meet their individual needs.
A survey of police departments conducted in 1997-98 (Mamalian and La Vigne et al., 1999) showed that only 13 percent of 2,004 responding departments used computer mapping. Slightly more than one-third of large departments (those with more than 100 officers) did so, but only
3 percent of small units did. On average, departments had used computer mapping for 3.3 years. Crime analysts were the primary users of mapping, with relatively few patrol officers involved. The types of data most likely to be mapped were:
The most frequent applications were:
- Arrests and incidents, including Uniform Crime Reports Parts I and II crimes.
- Calls for service.
- Vehicle recoveries.
- Automated pin mapping (point data).
- Cluster or hot spot analysis.
- Archiving data.