Profiling, Geographic

Geographic profiling is a methodology for delineating the probable area containing the residence of an unknown offender ostensibly responsible for a series of crimes. The probable area of the offender's residence stems from an analysis of the locations of a series of crimes. Therefore, geographic profiling can be used for a series of crimes or a single crime that contains multiple locations or scenes. Geographic profiling has been used mostly for serial homicides, rapes, and arsons, but its most vivid or notable application was with the DC Beltway Sniper cases during October 2002.

The idea of geographic profiling has been around since the mid-1980s, but it was not until the mid1990s that the idea was converted into operational software for development and testing. The method incorporates theories and concepts from a variety of disciplines and fields, such as cartography, computer science, environmental criminology, environmental psychology, geography, information science, mathematics, statistics, and transportation planning. There are several geographic profiling systems, but they all tend to model or imitate three specific or major systems. Each of these systems incorporates varying amounts of the theories and concepts from previously mentioned fields and disciplines.

All the geographic profiling systems share the same basic logic that is fairly straightforward, but the mathematics can be very involved. The locations for a series of crimes believed to have been committed by the same offender are plotted on a computer or digital map. A grid is placed over the entire area of the offenses. A series of mathematical functions known as distance decay functions are applied to the crime locations and to each cell of the grid. The distance decay functions approximate or model the travel behavior of the offender from his or her residence to the crime scenes. The resulting calculations create a probability value for each cell. When the cells are mapped with their varying probabilities, it is possible to delineate areas that have a greater likelihood of containing the offender's residence.

The premier geographic profiling system is Rigel, developed by Dr. D. K. Rossmo, then in Vancouver, British Columbia. This system incorporates and models important concepts and theories in environmental criminology pertaining to crime pattern theory, the routine activity space of offenders, and offender travel behavior. This system appears to be very popular with the law enforcement community because it was the first available and its creator was a former police officer. Moreover, this system has received considerable publicity.

Dragnet is another system that was created by Dr. David Canter in the United Kingdom. This system does not incorporate the exact theoretical base seen in Rigel and uses a restricted number of distance decay functions, but its major asset is that it is supposed to aid investigators in developing a practical search strategy for an offender. Finally, a third model, The Journey to Crime Routine, is part of the Crimestat suite of techniques authored by Dr. Ned Levine. This model provides a purely statistical solution to the problem of defining the possible area of an offender's origin. Moreover, this model gives the user the option of using a range of different distance decay functions.

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