These studies show that Geographic Information Systems (GIS) mapping can be a valuable tool for local officials, especially for jurisdictions that are contemplating the passage of residency laws. Officials can use the mapping data to determine whether affordable housing will be available in approved areas. Such analysis could demonstrate whether a proposed law is feasible. Localities with a residency law already in place can use the data to determine whether the restricted zones result in a lack of housing options for offenders. If unrestricted zones have sufficient affordable housing, offenders may be less likely to go underground and remain accessible to community corrections officers. Residency laws that limit where registered sex offenders may live have become increasingly popular with the potential impact of severely limiting housing options for these offenders and causing registered sex offenders to report false addresses, become homeless, or go underground. Studies in three States, New Jersey, California, and Ohio used GIS mapping to assess the impact of current laws or to project the outcome if a law were to be implemented. In all cases, from rural townships to intensely urban areas, they found that legal residential areas for sex offenders were severely limited. Results of these studies are summarized in this paper. 3 notes