The Strategies of Geographical Profiling
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What is the centre of gravity approach?
- Pioneered by Kind (1987)
- "Take a map of the area in which the 17 Yorkshire Ripper offences occurred and mark each location with a pin.
- Next take and 18th pin and join it to each of the 17 locations by a piece of thread.
- That location of the 18th pin which minimizes the amount of thread required is the centre of the 17 offences."
What are the problems with the centre of gravity approach?
- Provide only a single piece of information
- Can be distorted by spacial outliers
- Sometimes locations do not follow the rules of measures of central tendency
What is the circle hypothesis?
- Only used if the case suggests the offender is operating from a home base
- Offender is contained within a defined area
- Offender will move as little as possible but far enough away to avoid suspicion
- The home is central to the crime location
- Home range: area of activity space around offender's home
- Criminal range: area of offending between two offence sites furthest apart
What is the marauder type?
- Canter & Larkin (1993)
- Commit crimes with their home base central
- Leave the house and travel to commit
- Arsonists more likely to follow this pattern (82%) and 71% of Australian rapists (Kocsis & Irwin, 1997)
87% of rapists were found to be marauders
What is the commuter type?
- Canter & Larkin (1993)
- Offences are committed in areas believed to be unrelated to the area of residence and untraceable back there
- Areas for crime can be established as well as areas for their everyday lives
- Burglars more likely to adopt this strategy (Meaney, 2004)
- Athough 50/50 was found by Kocsis et al (2002) and at least 5 crimes were required before a perimeter could be established
What are probability distance strategies?
- Assume that the offender's crime site location is the same as their activity space and location
- A mathematical function is applied to each crime scene to generate a likelihood surface that indicated the probability of an offender living in that area
What are distance decay functions?
- Functions that state that the more geographically distance a location, the lower the probability of crime occurring there
- Calibrated using a calibration dataset, comprised of details of crimes committed in the area and travel patterns
- Each area has different travel patterns
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