Mapping applications for the millennium
Chapter 5: Synthesis and Applications

Crime mapping can be applied to the following criminal justice areas: criminal intelligence, crime prevention, courts and corrections, public information, and resource allocation and planning.

Criminal intelligence

Building criminal cases can be a painstaking process involving the compilation of information from diverse sources. All the data have a geographic dimension, although the importance of the locational information varies from vital to unimportant. Spatial data may provide answers to obvious questions about the crime scene, such as, Where is it?, but they also provide information for less obvious questions, such as, Where is this crime scene in relation to other relevant persons or objects? What locational information can be derived from victims, offenders, and witnesses? Can the geographic data be codified in the form of a map, and, if so, would such a map be useful to investigators? Investigators might map links between a suspect and his or her associates' home addresses to identify where the suspect's daily or weekly activities take place—the activity space. Another possibility would involve mapping gang graffiti as a way of defining gang territory.

Geographic analysis may be helpful on radically differing scales. For example, very large scale, or high-resolution, GIS could help with representing spatial data at crime scenes, such as the arrangement of objects in various rooms in a house or the pattern of crime in a highrise building in three dimensions (for more on this, see chapter 6). Other data may be better represented on a small scale—for example, facts relating to suspect movements in other cities or states. Depending on the importance of spatial information, a mini-atlas could be compiled, bringing together all the known geographic information and putting it in the context of other data.

Moland (1998) describes a case study in crime mapping in which a "cellular phone trail" was left by one suspect, providing an opportunity to plot spatial and temporal paths of two suspects. Detectives worked with telephone company technicians to verify that various antenna locations were working and to establish various aspects of cell phone signal patterns. One of the key pieces of evidence presented in court was figure 5.7, which shows cell phone antenna locations associated with the suspects' activities. This example illustrates not only the use of mapping to develop criminal intelligence, but also the use of mapping to develop courtroom evidence. The two men ultimately were convicted and sentenced to life in prison for a gruesome murder. Maps in the courtroom helped the prosecution walk the jury through a complex set of events by illustrating the collateral spatial relationships.

Figure 5.7

The information shown in figure 5.8 could also be used to document a pattern showing where and when incidents occurred based on the times of the related calls for service, as well as to provide information to corroborate information from witnesses.

Figure 5.8

As with any new technology, the risk of overselling GIS may lead to unrealistic expectations and dashed hopes. The best case scenario would include GIS as a useful contributor to the investigative process (see also the section titled, "Geographic profiling," in chapter 6).

Crime prevention

In a publication titled Preventing Crime: What Works, What Doesn't, What's Promising, Sherman et al. (1998) document "what works" for 11 crime problems. They identify approximately 30 actions or conditions as "promising." What is interesting about these lists is that many of the actions had little or nothing to do with policing. Many were amenable to the application of mapping tools, whether they were related to crime or other phenomena. This finding underscores that the label "crime mapping" is much too narrow a designation for what police departments do.

While some crime prevention actions were in the domain of schools or social service agencies, such as frequent visits by nurses to the homes of mothers and infants at risk, some were more directly connected to policing and had locational components that lent themselves to the application of geographic tools:

  • Nuisance abatement action on landlords of rental housing plagued by drug dealing. Where are the landlords? Where are the subject properties? What properties does a certain landlord own across a city? Once mapped, how can nuisance abatement action be planned to make the best use of both time and space resources? Can a network analysis program be used to optimize visits to properties?

  • Extra police patrols for high-crime hot spots. Where are the hot spots? How can patrol resources be optimized so that the patrol presence is proportional to the severity of crime in the hot spot? (Hot spots could be evaluated in terms of responses that allocate a fair share of the resources available on a given shift.)

  • Monitoring of high-risk repeat offenders by specialized police patrols. Where do released repeat offenders live? What does this pattern look like? Can repeat offenders be categorized or prioritized by the degree of risk they present, including the risk of repeating and the potential severity of the crimes they are likely to commit based on their histories?

  • On-scene arrests for domestic abusers who are employed or who live in areas where most households have an employed adult. Where are the salient locations? What are the home and work addresses of offenders? Can information on the current whereabouts of offenders and other locational data be maintained in a periodically updated registry?

  • Therapeutic community treatment programs for drug-using offenders in prison. This action recommendation reflects the work of Harris, Huenke, and O'Connell (1998). They used mapping to increase released offenders' access to services in Delaware, plotting locations of substance abuse, mental health, employment, and other social services, and relating them to the most recent addresses of probationers or parolees.

An example of a crime prevention program using geographic data in creative ways is the autodialer system employed by the Baltimore County Police Department in Maryland (Canter, 1997, 1998). Analysts subjectively identify clusters of incidents that have similar modus operandi and occur relatively close to one another (figure 5.9). Then a GIS is used first to randomly select telephone numbers in the ZIP Code area coinciding with the area under analysis, and second to further narrow down the numbers to the general area of the crime hot spot. The autodialer then calls all the telephone numbers on the list with a message from the police department relaying precautions to take and asking for reports of suspicious behavior. Experience shows that because some displacement of crime seems to occur, target polygons or areas must be expanded to take this displacement into account. Evaluation of the system suggests that it influences the actions of the community, the offender, and the police. Community awareness appears to heighten (911 calls reporting suspicious persons and vehicles increase significantly), and crime appears reduced, in spite of the moderate displacement effect.

Figure 5.9

Chapter 5: Synthesis and Applications
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Mapping Crime: Principle and Practice, by Keith Harries, Ph.D., December 1999