Crime mapping is a tool used by the police, other agencies in the criminal justice system, and researchers to visualize locations of criminal events and related phenomena. The practice of crime mapping has evolved over time from the plotting of points on paper maps by hand to the use of computer software programs known as geographic information systems (GIS). The following discussion of crime mapping will explore its development over time, major principles, practice, techniques, unresolved issues, and future directions.
Development over Time
The origins of the practice of crime mapping and spatial analysis of crime can be traced to the work of French sociologists Andre Guerry and Adolphe Quetelet in the early to mid-1800s. In the United States, principles of crime mapping and crime analysis hail primarily from the work conducted by sociologists in the early to mid-1900s at the University of Chicago. Now referred to as members of the ”Chicago School,” Robert Park, Ernest Burgess, Clifford Shaw, Henry McKay, and others performed research that comprises the basis for crime mapping today. Today, crime mapping is used by law enforcement agencies in many countries including Australia, Brazil, Canada, India, Japan, Norway, the United Kingdom, and the United States.
One of the earliest official examples of crime mapping in the United States is the Illinois Crime Survey of Homicides performed by the city of Chicago in 1926. The city of Chicago researchers reproduced the patterns of homicides via pin maps (Block 2000). What was most likely the first use of computerized crime mapping occurred in St. Louis in the mid-1960s (Harries 1999). Official recognition of the value of crime mapping by the U.S. federal government came in 1997 when the National Institute of Justice (NIJ) established the Crime Mapping Research Center (CMRC), now known as the Mapping and Analysis for Public Safety (MAPS) office. MAPS serves as a clearinghouse of information for crime mapping-related funding, research, software, conferences, and practice.
By the mid-1990s, computerized crime mapping became more widely used and accepted in large police departments, most notably by the New York City Police Department (NYPD) and the Chicago Police Department (CPD). COMPSTAT, computer-aided statistical analysis, for example, was first introduced to policing in 1994 by the NYPD. Since then many police departments have adopted the COMPSTAT program or developed a similar program. COMPSTAT has been heralded as a successful tool for law enforcement leading to increased communication between departmental units and outside agencies. The use of COMPSTAT by police is related to reductions in crime and improvement in community policing (Weisburd et al. 2004).
By 1998, 75% of law enforcement agencies performed at least some crime analysis but only 13% of those agencies used some form of crime mapping (Mamalian and LaVigne 1999). In 1999, approximately 11% of small police departments (fifty to ninety-nine sworn personnel) and 32.6% of large police departments (one hundred plus sworn personnel) had implemented a COMPSTAT-like program, with approximately 60% of departments with five hundred or more sworn personnel having implemented such a program (Weisburd et al. 2004, 6, 12).
Major Principles
Current techniques of spatial analysis of crime, including crime mapping, are based on an area of criminological theory known as environmental criminology. The theories of environmental criminology state that crime is predictably located in place and in time (Brantingham and Brantingham 1991). According to this perspective, the locations of crime can be explained through a number of factors, including the road and transportation network of a city and the ecological and demographic characteristics of places. Crime mapping is a natural tool, therefore, not just for law enforcement agencies, but also for criminologists.
Crime mapping relies principally on police data—calls for service and arrest data. Data used for crime mapping analysis must contain, at the very minimum, specific location data, incident types, and dates of occurrence. Accuracy of the data is of paramount importance. Without accurate data meaningful analysis cannot be performed. Before crime location data can be mapped, careful procedures must be in place to ensure the accuracy of recorded data and the thoroughness of recording (Casady 1999). In other words, for crime mapping to be a truly useful tool for the police there need to exist databases that integrate accurate and useful information from a variety of sources, the proper infrastructure to support it, and an efficient method for distributing the information to the officers and management (Manning 2001, 93).
Practice
Improvement in the capabilities of desktop computers is one explanation for the increased use of crime mapping by the police. The basic tool of crime mapping is the GIS. Modern desktop computer GISs permit the depiction and analysis of spatial phenomena in ways that were not possible before their widespread introduction. The ultimate reason for using a GIS is to provide a medium for geographic analysis. Traditional statistical analyses cannot do this.
A GIS spatially codes data and attaches attributes to the features stored to analyze these data based on those attributes. Data that are spatially coded have geographic coordinates associated with each data point. This process is called geocoding. The location of arrests may be coded to, for example, a street address, a zip code, or a police precinct, among other types of locations. A GIS is an increasingly flexible analytic tool that is limited only by the imagination of the analyst or researcher and the availability of spatially coded data.
Because a GIS organizes data in a way similar to maps it is an excellent tool for examining multidimensional, multifaceted crime problems. In other words, GISs are able to examine and clarify the spatial relationships that exist between general social indicators in an environment and the crime patterns that also exist there (Rich 1995). Due to their flexible analytic capabilities, GISs are used by the police for more than crime analysis and resource planning. GISs are also used for intelligence dissemination (Ratcliffe 2000, 315), to inform residents about crime problems in their area (Mamalian and LaVigne 1999, 3), and to support court testimony (Travis and Hughes 2002, 3).
A 1997 survey of law enforcement agencies in the United States found that of the departments that did not use GIS, 20% reported having budgeted funds to purchase hardware and software in the following year (Mamalian and LaVigne 1999, 1). The survey also found that of the departments that possessed crime mapping capability, ”. . . 88 percent use commercially available software packages, 38 percent have customized . . . application^], 89 percent use . . . desktop computers, 82 percent use the Internet [and] 16 percent use [Global Positioning Systems] to assist in their operations” (Mamalian and LaVigne 1999, 2). Ninety-one percent of the agencies reported mapping offense data and 52% reported mapping vehicle recovery data (Mamalian and LaVigne 1999,2).
An example of a sophisticated use of GIS for crime mapping is the Information Collection for Automated Mapping (ICAM) program used by the Chicago Police Department (Rich 1995, 1996). This system allows patrol officers to create their own maps. The ICAM system is easy for the officers to use; it requires only the use of a mouse where the officer selects the crimes of interest by clicking on incident types, districts or patrol beats, location types, and ranges of dates (Rich, 1995, 5; 1996). ICAM is installed in each of the district stations as well as in patrol cars.
Agencies other than the police use GISs to map crime. Two examples are the Wisconsin Department of Correction and the Office for Victims of Crime. The Wisconsin Department of Corrections uses GISs to map probationers and parolees as a means of targeting increased neighborhood supervision in areas where their residences congregated (Mixdorf 1999). The Office for Victims of Crime (2003) suggests the mapping of services for crime victims to compare them with the locations of crime victims’ homes.
Crime mapping is also used in criminological research to describe a number of different phenomena including, but not limited to, gang activity (Block 2000), drug arrests and interventions (Robinson 2003), crimes of serial rapists (LeBeau 1992), residential burglary (Rengert and Wasilchik 1985), and the home addresses of juvenile delinquents (Shaw and McKay 1969).
Techniques
Techniques of crime mapping are of two types, exploratory or confirmatory. Unlike exploratory techniques, which simply describe spatial and temporal patterns in the data, confirmatory spatial statistics explain the interdependence of spatial phenomena as well as their heterogeneity. To explore and confirm spatial patterns of crime, crime mapping generally assumes one of the following forms: point pattern analysis (electronic pin mapping), hot spots (clusters of crimes near to one another), and density mapping (for example, choropleth mapping uses color intensities to indicate crime density in places) (Vann and Garson 2003).
As technology improves and practical knowledge among analysts develops, techniques are increasing in complexity. Digital images (raster images) rather than simple point and line data (pin maps and street networks), temporal weighting (aoristic analysis—the recognition of patterns of crime based on time of day as well as in space), dasymetric mapping (for revealing patterns obscured with traditional choro-pleth mapping), and spatial autocorrelation (taking into account the criminogenic influence of adjoining places) are a few examples of the increasing complexity in current crime mapping techniques.
Techniques and tools for the mapping of crime for use by communities have also been developed. An example of this type of tool is the GeoArchive. A GeoArchive contains address-level data from both community and law enforcement sources, linked to a GIS capability (Block 1998). This tool brings crime mapping to community residents and multiagency task forces, thus allowing them to tackle their respective crime problems.
Unresolved Issues
Many agencies experience barriers to using crime mapping (Mamalian and LaVigne 1999; Rich 1995). These barriers include the acquisition of tools (computer hardware and software), technical expertise, sharing data across jurisdictional boundaries, duties of crime analysts, data accuracy, and data privacy issues.
The costs of computer hardware and software can be prohibitive to smaller departments (Rich 1995). Although street maps and maps of census blocks and census tracts are likely to be available from local and state agencies, if an agency purchases these maps from commercial sources, the financial costs can be high. A related issue to cost is training. Training personnel is costly. Without proper training for crime analysts and proper tools available for their use, including software and computer hardware, crime mapping will not be useful to the police.
Another unresolved issue involves mapping crimes across jurisdictional boundaries. Mapping across jurisdictional boundaries necessitates the sharing of spatial data between neighboring agencies. City limits and other boundaries can create artificial crime hot spots and can also limit the analytical utility of a GIS. Barriers to sharing data across boundaries often stem from political and organizational reasons rather than simply budgetary reasons (Eck 2002).
The type and quantity of duties assigned to crime analysts comprise a fourth unresolved issue in crime mapping. The amount of time a crime analyst spends conducting overall analysis for the department, generating reports, and responding to individual officer inquiries will affect the quality of analysis and crime mapping. Information technology (IT) can also become a problem for crime analysts, either when IT is not able to provide proper support to crime analysis software and hardware or when crime analysts are responsible for IT duties. Problems with IT can become a source of frustration for crime analysts (Ratcliffe 2000, 319).
A fifth unresolved issue involves data quality. Street maps become outdated on a regular basis, and a number of costs are associated with keeping them up to date. These costs can be financial in nature—for example, purchasing new software—but also involve personnel costs, to maintain the databases. Data recording lag time also affects the timely relevance of crime mapping reports. The amount of time between the filing of an officer report and accurate data entry affects the ability of crime analysts to provide useful information to their departments.
Privacy concerns are a sixth unresolved issue. The dissemination of spatial crime data can be problematic when the locations of crimes can be linked to specific addresses and, therefore, specific individuals. Police reports are public record. A number of police departments offer Internet crime mapping tools on their website. Suggested measures undertaken to address privacy issues when releasing crime data to the public include employing disclaimers, mapping to polygons rather than specific locations, eliminating exact street addresses, and limiting underlying information in data tables about the incident (Casady 1999).
Future Directions
The ”relative utility” of crime mapping to law enforcement will determine its viability as a resource (Travis and Hughes 2002, 4). To ensure continued use among law enforcement agencies, future directions and considerations for crime mapping include the following: professional standards, funding, global positioning systems (GPSs), data accessibility for patrol officers and for the public, cross-jurisidictional alliances, and crime forecasting.
The development of professional standards is a clear directive for the future (Wartell 1999). Standards may help to counteract misinterpretation of and misuse of information presented in maps (Idsvoog 1999). The amount of funding for the use of GIS by law enforcement agencies is a clear second future directive. To promote the use of GIS for crime analysis, funding will need to be increased.
A third directive for the future involves the use of GPS coordinates. GPS has many potential uses for law enforcement including locating officers to increase their safety and evaluating officers’ performance. GPS can also be used in conjunction with other place-related data and officer activities (Rich 1995; Travis and Hughes 2002). Corrections agencies have also begun to experiment with the use of GPS in electronic monitoring (Rich 1999).
The accessibility of spatial data to patrol officers is a fourth issue to be addressed in the future. If crime mapping is to be useful to the police, it must be available to patrol officers who can use maps to identify current problems or issues in the areas they patrol and to react accordingly. An example of where this type of crime mapping is being used is the ICAM system employed by the CPD. Fifth, the public should be granted increased access to crime mapping. A number of police departments currently offer crime mapping applications on their websites. Examples include the Portland (Oregon) Police Bureau, the Sacramento (California) Police Department, the Red-lands (California) Police Department, and the Austin (Texas) Police Department. Cross-jurisdictional alliances and collaboration between agencies at different levels of government comprise a sixth area to be addressed in the future in order to ensure the continued viability of crime mapping for crime analysis. The GeoArchive described earlier is an example of this. Last, crime mapping and analysis must focus on the development of methods to predict (forecast) crime patterns rather than simply display and explain current patterns.
Conclusion
Crime mapping is becoming widespread throughout law enforcement as technology improves and costs to purchase requisite software and hardware decrease. Whether law enforcement is able to overcome unresolved issues to allow crime mapping as a tool for crime analysis to realize its full potential remains to be seen.
