GIS

GIS is an acronym for Geographic Information System, a type of computer software that stores, manipulates, and displays maps and other spatial data. In forensic science, GIS software can be used to display and analyze patterns in maps showing crime scene locations, transportation routes, and potentially important forensic information such as bedrock or soil types. Some proponents have expanded the original definition of GIS to Geographic Information Science in reference to the body of knowledge about the techniques and applications of GIS software in addition to the software itself, but this article uses the original definition.

The October 2002 sniper shootings around Washington, D.C., are a high-profile example of a criminal case in which GIS software was used as a forensic tool. As the shootings occurred, detailed maps of the shooting locations were created and concentric circles were drawn at 1/4 and 1/2 mi (0.4 and 0.8 km) radii around the location of each incident. This allowed investigators to inventory buildings and other features that may have hidden the snipers, identify roads that the snipers may have used to arrive at or leave the scenes, and analyze similarities and differences among the shooting locations. At the time that two suspects were arrested, there were plans to expand the use of GIS to quantify the ease of access to each crime scene, analyze demographic and economic information about the areas in which the shootings occurred, and create three dimensional renderings of the crime scenes in order to identify similarities and perhaps predict the likely locations of future shootings. One of the difficulties encountered in this case was that the shootings occurred in different counties and states, and much effort was required to combine data from the different jurisdictions. Similar techniques have been used to solve serial rape cases in several large cities.

The use of geographic information to help identify suspects is known as geographic profiling. Although it is sometimes portrayed in the popular media as a highly developed discipline, geographic profiling is an imperfect practice that is continually evolving. Geographic profiling computer programs available in 2005 were based upon the results of research conducted in the 1980s and 1990s. The results suggested that most offenders commit crimes close to their homes; crime patterns follow a distance-decay function (the number of crimes committed decreases with distance from the offender's home); juvenile crimes are more highly clustered than adult crimes (because juveniles lack easy access to transportation); and the distance traveled varies according to the kind of crime. The output of geographic profiling programs consists of so-called hit score maps that use colored contour maps or three–dimensional surface maps to indicate the likelihood that a perpetrator lives in a certain area. Hit score maps can be combined with additional information, for example the addresses of known offenders or other suspects, and displayed using GIS software. Because of the amount of information required, geographic profiling works best in large cities where many crimes are committed. It can also require officials to recognize that a series of crimes are related and have likely been committed by the same person. Geographic profiling may fail in cases where a suspect travels great distances to commit crimes.

GIS software is also used by many agencies for so-called hot spot analysis, in which the locations of crimes such as murder, burglary, and auto theft are plotted on maps. Specialized computer programs available to law enforcement agencies can then be used to find clusters of crime scenes, or hot spots, that may help to identify areas for undercover operations or increased police patrols. Although the two share some similarities, hot spot analysis is different from geographic profiling. Hot spot analysis identifies locations in which crimes are committed whereas a geographic profile is intended to identify the person committing the crimes that, like hit score maps, can be linked to the home or work addresses of suspects using GIS software. GIS analysts can then add other information such as the location of forested areas that might provide an avenue of escape or the occurrence of soil identical to samples obtained from a suspect's shoes. Some jurisdictions make crime location data available over the Internet, allowing citizens to interactively query databases and produce maps of reported crimes or the registered addresses of convicted sex offenders.

When combined with global positioning system (GPS) receivers and transmitters, GIS software can be used to track the movements of criminals released on parole or probation to determine if they are related to newly reported crimes. GPS receivers installed in police vehicles can likewise transmit their locations and help to more efficiently dispatch law enforcement officials in the minutes after a crime has been committed. In 2005, some transit police in San Francisco were equipped with wireless personal digital assistants (PDAs) that allowed them to use GIS information while on foot or in trains and laptop computers for use in patrol cars.