Sex offender boundary restrictions:A geospatial approach

Michael ChajewskiFordham University

NIJ July 2008

Conceptual Framework

• Wetterling Act (1994): Mandatory Offender registration.

• Megan’s Law (1996): Community Notification.

• As of 2007 twenty-seven states had enacted some form of residency restrictions.

• Both state and local jurisdictions utilize residency restrictions typically ranging from 500 to 2,500 feet.

• Data can be complied from various sources (GPS tracking devices, Offender Registries etc.) and manipulated in several software packages (arcGIS, GRASS, GeoDa, R).

Territory

500 feet restriction

School

2500 feet restriction

Sex offendersnot in violation

Sex offendersin violation

Restricted Area

r

• r (radius) = 500 feet

• Area of circle = π r 2

• Area of a single 500 feet buffer = 785,398 feet2 (or 0.0282 miles2)

• Area of a single 2500 feet buffer = 19,634,954 feet2 (or 0.7043 miles2)

• Buffer zones, however, overlap and create larger polygons.

School

Territory

School

Calculated Distances

Streets

Sex Offender

Comparison

WebbElementary School

Webb Elementary School1375 Mount Olivet Rd NEWashington, DC 20002

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An Example

• Newark, NJ is generally included in analyses pertaining to the greater metropolitan area of New York City (mainly because of its accessibility and international airport).

• The population is roughly 273,546 people.

• There are 118 schools (K-12) in Newark, NJ (Essex County).

• As of June, 2006 there were 196 registered sex offenders within the city limits.

• A comparison set of 196 randomly selected residential addresses from the area have been selected.

Newark, Essex County, New Jersey

Newark, Essex County, New Jersey

In practice

• Boundary restrictions ought to apply to the population for which they are intended.

• Based on work by Hanson and Morton-Bourgon (2005) on average 13.7% of the sex offenders recidivated within the first 5 years. Recidivism impact cannot be evaluated and/or predicted based on residential geographic information alone.

• Residency restrictions as an alternative to monitor, control and supervise the sex offender population, as envisioned by policy makers, is extremely costly, labor intensive and invasive.

• Geospatial models used need to be carefully selected, justified, and analyzed (including error calculations, alternative approaches, plausible explanations, missing data evaluation; correlation is NOT causation).

• Other research looking at boundary restrictions: Julie Wartell (2007), Nobles et al. (2007), Grubesci et al. (2007; 2008).

Thank YouMichael Chajewski

chajewski@fordham.edu