Chapter 6: Crime Mapping Futures
Geographic profiling1 is an investigative methodology that uses the locations of
a connected series of crimes to determine the most probable area that an offender lives in. Although it is generally applied in
serial murder, rape, arson, robbery, and bombing cases, geographic profiling also can be used in single crimes that involve multiple scenes or other significant geographic characteristics.
Developed from research conducted at Simon Fraser University's School of Criminology and rooted in the pathbreaking work of Brantingham and Brantingham (1981), the methodology is based on a model that describes the hunting behavior of the offender. The criminal geographic targeting (CGT) program uses overlapping distance-decay functions centered on
each crime location to produce jeopardy surfacesthree-dimensional probability
surfaces that indicate the area where
the offender probably lives. The distance-decay concept (see chapter 1) conveys the idea that people, including criminals, generally take more short trips and fewer long trips in the course of their daily lives, which may include criminal activities. Thus
overlapping distance-decay functions are sets of curves expressing this phenomenon and suggesting, for example, that it
is more likely that offenders live close to
the sites of their crimes than far away. Probability surfaces can be displayed on both two- and three-dimensional color isopleth maps, which then provide a focus for investigative efforts (see chapter 1 for a description of isopleth maps).
This research has led to the development of Rigel, a computerized geographic profiling workstation that incorporates an analytic engine, GIS capability, database management, and powerful visualization tools. Crime locations, which are broken down by type (e.g., victim encounter, murder, and body dump sites for a murder), are entered by address, latitude/longitude, or digitization. Scenarios wherein crime locations are weighted based on certain theoretical and methodological principles are created next and examined. The addresses of suspects can then be evaluated according to their "hit" percentage on
a probability chart known as a z-score histogram, which can prioritize registered sex offenders, other known criminals, task force tips, and other information contained in databases.
Geographic profiling can be used as the basis for several investigative strategies. Some of the more common ones include:
- Suspect and tip prioritization.
- Address-based searches of police record systems.
- Patrol saturation and surveillance.
- Canvasses and searches.
- Mass DNA screening prioritization.
- Department of motor vehicles searches.
- ZIP Code prioritization.
- Information request mailouts.
Figure 6.1 displays the geoprofile produced from the analysis of 32 armed robberies that occurred over a period of approximately 12 months in the city of Vancouver, British Columbia, Canada. The purple areas around the periphery are less likely to include offenders' residences, and the yellow and orange areas in the center
are more likely to include offenders' residences. Three strategies were predicated on the geographic profile in this case. First, a search was conducted of the Vancouver Police Department's Records Management System for known robbery offenders who matched the criminals' descriptions and resided within the top 5 percent of geographic areas identified in the geoprofile. This did not produce any viable matches, as neither offender had had a previous conviction for robbery.
Second, a simplified geoprofile, displaying only the top 2 percent (0.7 square miles) of potential offender residences, was produced for patrol officers. Previous research determined that robbery offenders usually return home after committing a crime. It was therefore suggested that, in addition to responding to a crime scene after the report of a new robbery, patrol members should also search the most likely area
of offender residence, paying particular attention to logical routes of travel. This also was unsuccessful as the offenders were using stolen cars and no reliable vehicle descriptions were ever obtained (even though the geoprofile was used by police units to search for stolen automobiles that might be abandoned prior to a new robbery).
Third, the results of the geoprofile
were released on the television show "CrimeStoppers." This approach was successful, producing results that allowed the detectives to identify the offenders responsible for the series of robberies. The primary offender's address was located within
the top 1 percent of the peak area of
It is important to stress that geographic profiling does not solve cases, but rather provides a means for managing the large volume of information typically generated in major crime investigations. It should be regarded as one of several powerful decision support tools available to the detective and is best employed in conjunction with other police methods. Geographic crime patterns are clues that, when properly decoded, can be used to point in the direction of the offender.2
Currently, geographic profiling services
are available from the Vancouver Police Department, Geographic Profiling Section, Vancouver, British Columbia, Canada; the Royal Canadian Mounted Police, Pacific Region ViCLAS Section, also in Vancouver; and the Ontario Provincial Police, Behavioral Sciences Section, Orillia, Ontario, Canada. It will be available in
the near future from the British National Crime Faculty, Bramshill, United Kingdom.
Concerned about the mapping and prediction of serial crimes, Geggie (1998) reported on the work of Officer Timothy Meicher of the Los Angeles Police Department. The case related to robberies involving a perpetrator who rode a motorcycle and snatched purses from elderly victims in shopping center parking
lotshence the title "the Los Angeles Motorcycle Bandit." Employing basic
statistical conceptsmean and standard deviationMeicher produced a map with boundaries indicating two probability
levels for the next bandit strike, one at
68 percent and the other at 95 percent (figure 6.2). Meicher then collaborated with Geggie to automate the process of producing the probability map. Their model was subsequently distributed both inside and outside the Los Angeles Police Department.