Geographic Crime Mapping

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Crime Mapping

from The Encyclopedia of Criminology and Criminal Justice

Mapping crime has become a routine function of police departments throughout the world. All segments of the criminal justice system use aspects of crime mapping in their daily routine. In addition, crime mapping has been used to advance criminological theory.

· crime

· ecology

· environmental criminology

· law enforcement

· spatial analysis

Present day crime mapping is the application of a geographic information system (GIS) in order to understand crime data and the utilization of spatial analysis of crime situations in criminal justice agencies, especially in police work. Even though computer technology has been developed within the last century, the early crime mapping process goes back to the eighteenth century (Boba 2005). In one of the first instances of crime mapping, crimes against property and persons were plotted on a map in reference to the level of education of the offenders in France. The process of mapping crime was later used in England to study crime situations using area characteristics, such as urbanization and highway proximity (Paulsen and Robinson 2004).

The practice of crime mapping was initiated in the United States in the early 1920s by the Chicago School. It was done for the purpose of studying the factors behind juvenile delinquency in Chicago. All crime mapping in these early years was done by hand and continued to be done by hand for many decades. It was not until the early 1960s that computers were used to help with the process. In the 1980s the advent of client server technology made GIS more accessible to the police and research communities. For instance, the National Institute of Justice teamed up with researchers and practitioners in five cities (Jersey City, Harfort, San Diego, Pittsburgh, and Kansas City) to use innovative tools in studying drug markets and tracking their movements over time.

Since the 1990s, with the advancement of computer technology as well as police data systems, crime mapping has become a more accessible and practical tool for police practitioners and researchers. GIS software can be installed on desktop computers that have sufficient power to process a large batch of data in seconds. It was during this period that data on crimes, arrests, accidents, and calls for service became available in an electronic format, through either electronic dispatch systems or records management systems. Recent developments in digital mapping (including affordability) and technological advancements in policing have enabled environmental criminologists to explore the special dimensions of criminality in comprehensive ways using crime mapping.

The crime mapping process requires elements of a computer system not much different from other computerized processes. These are computer hardware, software, data, peopleware, and work procedures involving organization policies, safety protocols for the system, and so on. However, there are some requirements specific to computerized crime mapping. For example, certain devices may be needed in the working process (such as a digitizer, a plotter, and a GPS—global positioning system—device). People working in crime mapping should be equipped with backgrounds in GIS technology or have access to a GIS specialist, if needed.

Software products for crime mapping are quite numerous. Some have been created specifically for law enforcement uses, including Crime Stat and RAIDS. Other programs are geographic information software that can be used for the general purpose of mapping. Like other types of software, software for crime mapping can be divided into two categories: open source and proprietary. Open source mapping software is available to any user for little or no fee, and includes such programs as GRASS GIS and SAGA GIS. Proprietary mapping software must be purchased from the provider and includes ArcGIS, Map 3D, and Bentley Map, among others.

Creating a crime map incorporates working with data layers. Data involved in the mapping process consist of three parts. The first part is the structure of the layout which is the base map. It contains the basic information (points, lines, and polygons) that make up a map, just like a common map. This base map can be used for mapping in police work, as well as for other purposes of mapping, depending on the user's needs. The second part, crime data, includes the location and details of the crime incidents that the users intend to incorporate into the crime map. These details may include incident type, date and time of the incident, address or location of the incident, property loss, and so on. This information can be stored in and retrieved from a separate data server or at the same location as the other data used to create the map. The last part is any other data which the users decide to show in the crime map, including points of interest, links to other media (e.g., video clip, audio file, and picture), and other information useful for presenting the map so that it can more easily be understood by viewers.

The process of making a crime map involves putting the data layers together. Recent advances in computer technology, relevant software, and digitized data make it possible to create a crime map digitally. One process crime map creators often need to operate is geocoding, which is the process of transforming the locations of crime data into geographic coordinates, usually in the form of latitude and longitude, ready for crime mapping software to utilize. A geocoder, which could be a piece of software or a web service, can do the transformation for the researcher. Crime mapping always involves a large amount of crime and geographic data (more than 10,000 data points are not unusual), making a geocoder a very useful tool. The process of transforming crime locations into coordinates is called address interpolation.

Many theories of crime try to explain individual or group criminal behavior and ignore other contributors to crime, including the environment. Theorists who want to include environmental factors to explain crime have begun to see crime as an event—not just a product of an interaction between people, but an interaction between victims, offenders, and their environments (Paynich and Hill (2009): 97–118). Paynich and Hill mention that after researchers began to examine the contributions of time and space to criminal events, crime mapping became an important tool for both crime fighters and criminologists.

Ecological theories look for explanations of individual actions in general features of the social structure in which an individual is embedded. The social ecology perspective evolved from the early social ecologists in France in the mid 1800s, to the Chicago school in the 1920s, and finally to a recent revival in contemporary studies in the ecology of crime. The social ecology perspective developed into more specifically focused, place-based theories of crime, particularly routine activities theory.

Bernard Cohen did a study (1980) on street-level prostitution and identified “hot spots” of prostitution activity. Cohen's work is one of the first empirical studies to document the spatial and temporal intersection of “motivated” offenders and the crime-facilitating properties of place proposed by the routine activities theory theorized by Cohen and Felson (1979). Modern GIS capabilities, combined with point data on the locations of individual crimes, make studies like those described here feasible by enabling researchers to routinely obtain measures of crime variables at these nontraditional and smaller levels of aggregation. Consequently, several different theoretical approaches have been made possible, including place-based theories derived from routine activities theory (Cohen and Felson 1979) and rational choice theory (Cornish and Clark 1986), crime pattern theory (Brantingham and Brantingham 1993), and Crime Prevention Through Environmental Design (CPTED).

Mapping crime has become a routine function of police departments throughout the world. Moreover, all segments of the criminal justice system, from courthouses to correctional institutions, from the probation officer's desktop to the operation commander's handheld, uses a variety of crime maps. Hot spot to offender behavior, susceptibility analysis to density analysis, and other crime mapping procedures are part of their daily routine (Can and Leipnik 2010). Similarly to other general types of data, crime maps can be used by law enforcement to present crime information in many ways. One way to classify the maps used by law enforcement is to look at it from a crime analysis standpoint. Crime analysis aligns mapping used by law enforcement into three basic areas: administrative, strategic, and tactical (Paynich and Hill 2009). Under these areas, six categories of mapping types are commonly used: single-symbol mapping, buffers, graduated mapping, chart mapping, density mapping, and interactive crime mapping. Single-symbol mapping, as suggested by its name, utilizes one type of symbol to represent features (e.g., locations of police stations, schools, incidents, and so on). This type of mapping is not suitable for data with multiple incidents occurring at the same specific locations. A buffer map displays a specific area surrounding a feature, making it possible to find other features located in that area. It is suitable for analysis purposes. For instance, an analyst can use a buffer map to show the number of drug-related incidents occurring within a distance of 1,000 feet from schools in a county during a six month period. Graduated mapping utilizes different sizes or colors of features to represent particular values of variables. Differences in size or color reflect variation in value. Chart mapping incorporates charts (pie and bar) into the map. Density mapping conveys the frequency of incidents in specific areas through color shading, with darker colors representing more incidents. Interactive crime mapping is usually offered to users via internet by police departments. The interactive functions enable users, police and citizens, to conduct some basic crime mapping independently. (See Figures (1, 2, 3, 4).)

Source: Salih Can and Prapon Sahapattana.

Locations of murder incidents in police precinct 67, Brooklyn. The map indicates that there were 50 murder incidents in the precinct in recent years. Of these incidents, 26 (52%) occurred at avenues.

Source: Salih Can and Prapon Sahapattana.

Weapon distribution of murder incidents in police precinct 67, Brooklyn. Of the 50 incidents, 46 (92%) were committed with a handgun, two with a blunt instrument, one with a knife, and one by fire.

Source: Salih Can and Prapon Sahapattana.

Victim gender distribution of murder incidents in police precinct 67, Brooklyn. Victims were male in 44 (88%) incidents and female in 6 (12%) incidents.

Source: Salih Can and Prapon Sahapattana.

Locations of murder incidents in police precinct 67, Brooklyn. Outside buildings, 29 (58%); inside buildings, 19 (38%); no data, 2 (4%).

Two approaches to analyzing crime situations are using exact locations of incidents to generate hot spots of crime and using tabular data and statistics to show the analysis. “Hot spots” are concentrations or clusters of crimes in space. There are three fundamental ways of identifying crime hot spots; visual inspection, statistical identification, and the theoretical approach. Crime can be mapped in areas or layers (for instance, by socioeconomic status, traffic intersection, or location of places) and then put on top of each other. Viewing these layers together makes it possible to see the natural patterns of movement for the people who use the area, the location of potential offenders, and likewise potential targets. This provides a reasonable initial explanation for a concentration or clustering of crimes. Brantingham and Brantingham (1999) find it helpful to describe these levels or layers of crime potential as the environmental setting, with a more detailed description of normal movement patterns, location of potential crime generators, location of potential crime attractors, characteristics of place, and ecological labels. Hot spots are also directly related to structural setting, which is composed of relatively slowly changing elements (e.g., laws, social norms, class structures, the division of labor, the physical layout of the built environment, the local topography, the local climate, and so forth) and the activity setting, which is composed of routines and adventures. The activity setting is shaped by mobility and awareness factors that are tied to personality, age, social status, income, education, and a variety of other social and psychological characteristics, as well as to positioning in physical space-time.

For purposes of analysis, a statistical classification is beneficial for crime analysts both to understand the crime situation and to present the situation to the audience. That is, the data in focus will be categorized into groups for investigation. A statistical classification is used in crime mapping in order to determine how the data on the map will be displayed in the way that is helpful to the viewers to more clearly understand the data. Generally, four statistical classifications can be found in the crime mapping process: natural breaks, equal interval, quartile, and standard deviation. The type of classification is commonly exhibited in the legend of the map.

Natural breaks classification is the default in many geographic information system programs and also the most popular in crime analysis. Generally, it is exercised to explore the data first and also to obtain a quick analysis of the data. Equal interval classification could be used by a crime analyst for data with the same number of incidents in each interval. The nature of crime incidents, however, does not follow this pattern. Consequently, this type of classification is not often used for the final crime map. A quartile map is used for comparison between data sets in different maps. In each map, the different symbols are displayed in order for viewers to see the crime situation on the map. Finally, a map using the standard deviation classification involves utilizing the means and standard deviations of the data to establish the break points of the groups. This type of map is useful for comparison purposes between different data sets. Finally, an analyst could use a manual method to decide the break points. The method utilized to create a map and how many categories to use, should be determined by the analyst, according to the purpose of and audience for the map.

Crime mapping is unquestionably salient and accepted among law enforcement agencies. Mapping crime data, as well as data related to disorder problems, enables police officers to learn the location of crime or disorder incidents. It also reveals the reasons behind the problems through the process of crime analysis. Research shows that a great number of large police departments have been using computerized crime mapping for almost 15 years (Mamalian & LaVigne 1999). Research also confirms the use of computerized crime mapping by small departments, as well. They use crime maps for staff allocation decisions, evaluation of intervention programs, informing citizens about crime situations in their neighborhoods, and identification of repeat crime locations, as well as for calls for service.

The rapidly decreasing price and user friendly nature of desktop computers and GIS software has made crime mapping much more prevalent. Currently, the integration of crime mapping with GPS has increased the accuracy of the incident locations. People are increasingly familiar with the integration of crime mapping due to web-based applications and multimedia, such as audio, video, and pictures. Adding advanced statistical programs to the picture, more sophisticated analyses are rendered more advantageous to officers and citizens. The trend of crime mapping, as well as crime analysis, is likely to continue to grow in law enforcement agencies, especially as new technologies to enhance the utility of this practice are developed.

References

 Boba, R. (2005) Crime Analysis and Crime Mapping. Sage Thousand Oaks CA.