Tracking and Spatial Analysis of Sex Offender Movements


“The California Department of Corrections and Rehabilitation (CDCR) has begun tracking more than 6,000 sex offender parolees by using global positioning system (GPS) anklets. Sex offender parolees are allowed to travel only through certain areas and must keep away from other people. The GPS device lets parole agents know when parolees are somewhere they should not be by logging GPS coordinates every minute and sending coordinates to a central server every 10 minutes. This information about parolee location is compared to law enforcement incident data through crime-scene correlation reports. Regular e-mail reports keep analysts notified of any incidents that are close to an offender’s tracks in time and space. The features are accessible through an online mapping application, and analysts can review a parolee’s GPS data for up to 4 hours at a time, or view data in real time (with a 15- minute delay).

“Keeping track of parolees’ movements can take a lot of time and law enforcement resources. Law enforcement and parole agencies need a way to sum vast amounts of spatial behavior and coordinate it with related crime information. Environmental Systems Research Institute’s (ESRI) Modelbuilder and the kernel density tool are essential for analysts who track and analyze sex offender movement data.”