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Geographic Information System (GIS):

As recent improvements have been made in computer technologies, law enforcement agencies have looked for a variety of ways to apply these technologies in order to improve their operations. Computers are rapidly becoming an indispensable tool to aid in crime analysis. Current technologies make it easy for an agency s computer system to "geocode" data to improve the degree of analysis. This process allows organizations to analyze what they know about the nature and extent of crime in their jurisdiction, which in turn allows for improved resource allocation. A Geographic Information System (GIS) is perhaps the most common way for agencies to enhance their analytical capabilities using computerized mapping.


A Geographic Information System introduces a spatial or geographic component to a database. Every case in a data set includes a reference to that case s location in relation to the Earth or a smaller scale (such as a map). For example, a landowner could record what types of trees are located on a one acre parcel of land, including their relative location. This would allow the landowner to develop a detailed map of the land.

Measurements would reflect how far each tree was from a specific point on the property (such as the center of the parcel of land). After locating the center of the property, the owner could note an oak tree ten feet to the north and three feet to the east of this center reference point. In other words, in addition to noting that there is an oak tree on the property, the landowner has "geocoded" the tree s spatial location.

This is essentially how geographers record different features all over the world and how the military develops targeting information. For example, a map can be created which identifies various military and industrial targets suitable for attacks. In the event of a planned attack on Country X, the military might know that there is an airbase at a specific latitude and longitude which they want to eliminate. A GIS allows a user to link a set of information (an elm tree or an airbase) with its spatial or geographic position.


As a tool for law enforcement, GIS allows police agencies to create visual representations of crime and social problems within their jurisdiction. An agency must first develop an adequate "base map" of their jurisdiction. Base maps reflect the most essential information about a parcel of land for a particular application. For law enforcement applications, a GIS base map would certainly reflect roads and streets.

Some agencies might also want their base map to include alleys, major waterways, railroad lines, public transportation routes (i.e., subway or elevated train routes), or bicycle/foot paths. The information contained in a base map is determined by the needs of an agency and the nature of the jurisdiction it serves.

Stated simply, once a base map has been properly developed, it is possible to instruct a computer system to automatically geocode the location of calls for service, reported crimes, and other police activities. Every time a street address is entered into the location field of a computerized incident database, geocode information is automatically generated to link the information about that address to a specific point on the base map. Depending upon the nature of a specific system, this geocode might reflect a global position (a point s latitude and longitude) or a relative spatial position (a point s location in relation to a fixed reference point, such as the center of a city or a specific corner of a county s border).

Once an agency has developed a base map and created the capacity to geocode location information, mapping software can be used to plot police activities, community problems and other information on a map of a jurisdiction. Using mapping software, it is remarkably simple to visually display geocoded information in a number of different fashions. A map can be generated to pin point exactly where different offenses have occurred (called a "point" map), much like the pin maps once used to aid crime analysis. An example might be a map showing all of the burglaries reported during a three month period. Such a map might allow police personnel to identify trends and patterns in burglaries.

A variety of crimes can be reflected on the same map by using different point markers to reflect the location of different types of offenses (much like different colored pins were used in the past). A small car reflects a stolen auto, a small handgun represents an armed robbery, an "H" in a box indicates a homicide.

There is not a universal key for such point markers; the possibilities are endless and depend on the creativity and needs of individual departments. Alternatively, maps can be generated to show the level of crime or activity in different areas (a "theme" map). For example, a map could be generated to use different shades of reds to reflect the level of serious crime in different neighborhoods, beats, or precincts. Deep reds would might reflect a high level of serious crime, light reds a more moderate level, and pink or white a low level. Such a map would allow for the identification of "hot spots" for serious crime in that particular jurisdiction.

The decision to use either a point map or a theme map depends upon a user s needs and their right to private information. An officer creating a map to help determine resource allocation might prefer a point map because it will offer the officer a higher degree of precision. An officer creating a map to reflect crime in different parts of the city might prefer a theme map, which often is better at reflecting the "big picture." If these maps were to be given to citizens, it may certainly be more appropriate to use a theme map. A point map showing the location of sexual assaults may violate a victim s right to privacy if the map would allow someone to determine a precise location of an offense.

It should be noted that some mapping software can be instructed to randomly off-set the location of a point marker in order to avoid such situations. The Lansing (MI) Police Department is in the process of applying GIS technology on the agency webpage. Users will be able to generate a crime map for their neighborhood. The maps will randomly off-set the location of point markers to make it difficult for the public to know exactly where an offense occurred.

Citizens can still have an idea of crime in their neighborhood, while the privacy of victims is still protected. Using GIS technology, producing a map to plot crime, activities, or other data is similar to making a pizza; what you order depends on your needs. Like a pizza, crime maps can be ordered in a variety of sizes, depending upon your "appetite." You can generate a large (jurisdiction-level), medium (precinct-level), or small (beat-level) map; the size you choose depends upon what you need the map to represent and how much detail you require. In addition, software can be modified to allow users to select a vast number of ways to "top" their pizza (these "toppings" are usually called "layers"). The number and variety of layers is determined by the creativity and the needs of those responsible for managing a department s GIS.

For example, a user could be given the option of selecting what categories of offenses (personal, property, disorder) or specific types of offenses (theft, stolen auto, robbery, burglary) are shown on a map. Users can be given the option of selecting the time frame reflected in a map (offenses in the past week, two weeks, or the month of June), or of selecting only those offenses occurring during certain times of the day. A supervisor for a special operations unit could identify potential "hot spots" in order to determine how to deploy officers.

Trends in specific types of offenses can be tracked across time, such as fluctuations in residential burglaries in the month of December in the past five years. A user could visually determine whether a particular program (i.e., an effort to reduce street-level prostitution) had any impact on the targeted offense.

With more advanced systems, an infinite number of layers could be made available to users, depending on resources, needs, and the nature of the jurisdiction served by the agency. Possible layers might include the location of mass transit routes, pay phones or automatic teller machines, half-way houses, schools, business districts, parks, or churches, just to name a few. Law enforcement organizations can exchange data with other criminal justice agencies in order to use GIS to link crime data with the location of juveniles on probation, registered sex offenders, or persons on tether. Linking data on reported crimes and the location of known offenders can aid in crime analysis and investigative functions. Each of these different layers represents a different topping a user might decide to place on their pizza (or map); this allows the user to customize the final size and toppings for a pizza to suit their appetite and their individual taste.

Current mapping software are generally Windows-based, making their use quick and easy. Although the creation and maintainance of a GIS package requires some expertise, any police employee can be trained to generate maps in just a few hours. An officer equipped with a computer and (ideally) a color printer can produce an informative map in a matter of minutes. Some software allows system administrators to offer different layering options to different types of users. Civilian crime analysts might have full access to extensive layering options. Patrol officers might have access to less extensive list of layers, while still having the ability to create customized maps to meet their needs. Citizens could be given an extremely basic list of layers (perhaps just selecting the type of offense(s) they wish to map) via the Internet.

At the most basic level, GIS is nothing new to police organizations. Agencies have used pin maps for decades as a means to visually explore crime in their jurisdiction. GIS offers users with the opportunity to convert basic pin maps into a powerful tool for planning and management. Users can instantly create countless customized maps to meet their unique needs. Crime maps are no longer static representations of the past; instead, they are dynamic applications which can help police agencies serve their communities in a significantly more effective and educated fashion.


A GIS program is only as good as the accuracy of its maps and its geocode systems. Departments establishing GIS need to make sure that their base map is accurate and is updated on a regular basis. Agencies might check with other city or county government departments to find out if a suitable base map is available.

Geocoding programs must be able to correctly interpret different ways of expressing the same location. For example, can a program know that "100 E. Elm", "100 East Elm", and "Elm and Main" are all the same location? In using theme maps, misleading "hot spots" can be inadvertently generated. GIS might assign a location geocode based on where a crime is reported, as opposed to where it occurred.

Preview image of a GIS screen.
Preview of GIS Screen

Any patrol beat or neighborhood where there is a hospital or a police facility could appear to be a hot spot, even though the offenses actually occurred elsewhere. All users of an organization s GIS need to understand exactly what that system is telling them about crime and disorder.

Finally, agencies must remember that GIS is only as good as the information put into the system. For example, does you data base include only calls for service and officer-initiated activity; if so, does that accurately reflect the level of crime in your community? GIS is inherently limited because it only reflects crimes known to the police; high crime areas where residents do not report many offenses may appear to be low crime neighborhoods on a GIS map.

Agencies must always be mindful of what their geocoded database actually reflects.