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While the problem analysis triangle (Step 8) identifies the three essential elements of crime, it does not explain how offenders find suitable targets. According to Marcus Felson, they do this in three main ways:
Through personal knowledge of the victim (your neighbor's son might know when you are away from your house).
Through work (a burglar working as a telephone engineer might overhear that you will be taking vacation next week).
Through overlapping "activity spaces."
The concept of activity spaces is central to crime pattern theory, which was developed by the Canadian environmental criminologists Pat and Paul Brantingham (see figure). They use the concept to describe how offenders find targets in the course of their daily routines. Starting with a triangle, they consider offenders going from home to work to recreation. Around each of these three nodes and along each of these three paths (excepting a buffer zone where they might be recognized) offenders look around for crime opportunities. They may find these a little way off the path, but they usually do not go far beyond the area they know. This is because it is easier to commit crimes in the course of their daily routine than by making a special journey to do so.
The Brantinghams also use the term edges to refer to the boundaries of areas where people live, work, shop, or seek entertainment. Some crimes are more likely to occur at these edges - such as racial attacks, robberies, or shoplifting - because this is where people from different neighborhoods who do not know each other come together. In an early study, the Brantinghams found that residential burglaries in Tallahassee, Florida tended to cluster where affluent areas bordered on poor areas. Their explanation was that the affluent areas provided attractive targets to burglars from the poorer areas, but the burglars preferred not to venture too far into them because they were unfamiliar with the territory and might be recognized as not belonging there. They would also be more vulnerable because they would have further to travel with the proceeds of the crime.
The paths that people take in their everyday activities and the nodes they inhabit explain risks of victimization as well as patterns of offending. This is why the Brantinghams and other crime pattern theorists pay so much attention to the geographical distribution of crime and the daily rhythm of activity. For example, these researchers generate crime maps for different hours of the day and days of the week, linking specific kinds of crimes to commuter flows, school children being let out, store closing hours, or any other process that moves people among nodes and along paths. Pickpockets and some shoplifters seek crowds, while other offenders pay closer attention to the absence of people. For example, the flow of people to work generates a counterflow of burglars to residential areas, taking advantage of the commuters' absence. The flow of workers home at night and at weekends produces a counterflow a few hours later of burglars targeting commercial and industrial sites.
Many studies have shown that the journey to crime is typically very short - offenders generally commit crimes within 1 or 2 miles of their homes. For example, Andy Brumwell, a crime analyst with the West Midlands Police, one of the U.K.'s largest police forces, has recently completed an analysis of 258,074 crime trips made over a 2-year period. He found the following:
Susan Wernicke, a crime analyst with the City of Overland Park, Kansas, presented more detailed information on juveniles at the National Institute of Justice's 2000 National Crime Mapping Conference in San Diego, California. She showed that in Overland Park the 11-yearolds arrested had committed crimes an average of 1.05 miles from home. This distance gradually increased with age, and by age 17 was 2.7 miles. She attributed part of the increase to greater access to cars.
Andy Brumwell has developed the "self-containment index," which looks at the percentage of crimes in an area that is committed by offenders who also live in that area. A value of 100 indicates that local offenders are responsible for all the crimes, whereas a value of zero indicates that local offenders commit none of them. This value should be calculated when analyzing a local problem. Whether predators are local or come from a distance will have an influence on the type of situational crime prevention measures that could be successfully introduced. For example, closing streets in a particular neighborhood will only be effective if many of the offenders drive to the neighborhood to commit crime.
You can use the concepts of crime pattern theory to understand crime in your jurisdiction. You should try to piece together offender and offense patterns by finding nodes, paths, and edges. You can begin to distinguish between how offenders search for crime and when they find it by accident. You can find where offenders are absent and where they congregate in hot spots and think about the reasons for this (Step 17). You will find that very local crime patterns tell the story. Thus a high-crime district will have some streets with no crime at all and some addresses which generate most of the problem. Residents may know it is fairly safe to walk down one street but not to walk down another. They may even choose one side of the street over the other. If residents know their local turf this well, what's to stop you from finding out about it? Crime pattern theory helps you do just that, and it will help to define a specific problem at the scanning stage and understand the contributory causes at analysis.
Kim Rossmo prepared this diagram to represent the Brantinghams' theory. It shows an offender's activity space (residence, work, recreation, and the travel routes between them), the buffer zone close to the home in which offenders do not usually commit crimes, and five potential target areas (for example, parking lots). Where an offender's activity space intersects a target area, this is where crimes happen (crosses). Note that in this example no crimes occur around the offender's workplace, because there are no suitable targets there. Also, there are two target areas with no crimes in them because this offender is not aware of those places.
Source: Rossmo, Kim (2000). Geographic Profiling. Boca Raton, FL: CRC Press.