The Journey-to-Crime Buffer Zone: Measurement Issues and Methodological Challenges

The journey to crime is a well-researched phenomenon in environmental criminology. Various studies have measured the distance between criminals' homes and their crimes, while examining the influences of offender and offense factors. Other research has explored the nature and characteristics of criminal travel distributions, including changes in offending probability by distance. This last requires an understanding of the shape of the journey-to-crime function, particularly its key components of distance decay (offending probability decreases with distance) and the buffer zone (a lower probability area surrounding an offender's home). However, it is difficult to study the shape of these distributions because of the data requirements. This article offers an overview of the buffer zone, its definition and characteristics, and two proposed explanatory theories. We then outline four critical research considerations and the ecological fallacy problem. Finally, we propose a testing procedure for the presence of a buffer zone in a sample of individual-level crime trips. Using simulation analysis, we conclude 50 or more observations are needed to reliably determine the shape of an offender's travel distribution, a number much higher than found in previous studies. We provide two case studies of prolific predatory offenders that show strong evidence of the buffer zone.