Crime Mapping PDF

CHAPTER IV CRIME MAPPING - Crime Mapping – Historical Development of Crime Mapping; Theories of Crime; Place and Environmental Design; Types of Crime Mapping and Crime Analysis; Crime Incidence Situationer, and the Geographic information of crimes Crime mappi...

CHAPTER IV CRIME MAPPING - Crime Mapping – Historical Development of Crime Mapping; Theories of Crime; Place and Environmental Design; Types of Crime Mapping and Crime Analysis; Crime Incidence Situationer, and the Geographic information of crimes Crime mapping Crime mapping is a tool used to identify and highlight suspicious incidents and events that may require further investigation. In addition crime mapping helps individuals to understand events and dynamics in a neighbourhood including person, events and hazards. Maps increase the knowledge of existing problems present in a territory (Patricio Tudala 2004). They allow the identification of hot spots and the destination of resources to areas with more needs and not to the ones with low priority despite of resident’s pressure. Crime mapping also helps investigators to identify suspicious offenders and suspects of crime thus increasing investigative suspect list based even when no lead is evident. “a progressive blend of practical criminal justice issues with the research field of geographical information systems and science” (Chainey and Ratcliffe, 2005) It exploits the inherent geographical quality of crime – Where do offenders live? – Where are the most vulnerable communities/targets located? – How do offenders travel to the crime location? – Why do crimes occur in one area and not another? – Where are our emerging problem areas Crime Analysis Mapping (Boba, 2001) “Crime mapping” is a term that has been used for the past few years to refer to research analysis using GIS in a law enforcement setting. In this report, the term crime analysis mapping is used to describe this process because using a GIS to analyze crime is not just the act of placing incidents on a map but also of analysis. Consequently, “crime analysis mapping” is: The process of using a geographic information system in combination with crime analysis techniques to focus on the spatial context of criminal and other law enforcement activity. Crime mapping serves three main functions within crime analysis: 1. It facilitates visual and statistical analyses of the spatial nature of crime and other types of events. 2. It allows analysts to link unlike data sources together based on common geographic variables (e.g., linking census information, school information, and crime data for a common area). 3. It provides maps that help to communicate analysis results More Definitions (Wilson & Filbert) The term “crime mapping” is inaccurate as it is overly simplistic. Crime mapping is often associated with the simple display and querying of crime data using a Geographic Information System (GIS). Instead, it is a general term that encompasses the technical aspects of visualization and statistical techniques, as well as practical aspects of geographic principles and criminological theories. From a technical standpoint, the term is a combination of visualization and statistical techniques manifested as software. This combination of techniques is shared between mapping, spatial analysis and spatial data analysis. Mapping is simply a visualization tool that is used to display raw geographic data and output from analysis, which is done through a GIS. Spatial analysis is the statistical testing of geographic features in relation to other geographic features for patterns, or lack thereof. Spatial data analysis is the combination of spatial analysis with associated attribute data of the features to uncover spatial interactions between features. From a practical standpoint, crime mapping is a hybrid of several social sciences, which are geography, sociology and criminology. It combines the basic principles of geographic analysis, sociological and criminological theory and makes it possible to test conjectures from these disciplines in order to confirm or refute them as actual. In essence it has developed into an applied science, with its own tools, that examines a range of issues about society and its relationship with the elements that contribute to crime. Thus, crime mapping is interdisciplinary, involving other disciplines that incorporate the spatial perspectives of social phenomena related to crime, such as inequality, residential stability, unemployment, resource depravation, economic opportunities, housing availability, migration, segregation, and the effects of policy. Using a geographic framework often leads to a more comprehensive understanding of the factors that contribute to or suppress crime. Even though the term “crime mapping” is a misnomer it will continue to be widely used as a general term with regard to the study of the spatial aspects of crime. Users of the term need to let the context of their work dictate which standpoint is being referred to A geographic information system is a set of computer-based tools that allows the user to modify, visualize, query, and analyze geographic and tabular data History of Crime Mapping ( Boba, 2005) Even though crime mapping plays a significant role in crime analysis today, conducting spatial analysis and creating crime maps have only recently become common in policing and crime analysis, thanks to advancements in technology. Unlike crime analysis, the history of crime mapping begins not with the establishment of the first police force, but with researchers long before computers were invented. Beginnings of Crime Mapping In the 1800s, European researchers who adhered to the school of thought known as the cartographic school of criminology examined the levels of crime within different areas (regions) and the relationship of these levels to sociological factors, such as socioeconomic status (Groff & La Vigne, 2002). For example, in 1829, Adriano Balbi, an ethnographer and geographer, and André-Michel Guerry, a lawyer, created the first maps of crime using criminal statistics for the years 1825 to 1827 and demographic data from the census. They examined crimes against property, crimes against persons, and levels of education in France and found that areas with high levels of crimes against property had a low incidence of crimes against people and that higher numbers of educated people lived in areas with more property crime (Weisburd & McEwen, 1997). Also during this period, the Belgian astronomer and statistician Quételet used maps to examine correlations between crime and transportation routes, education levels, and ethnic and cultural variations (Weisburd & McEwen, 1997) United States: 1900–1970 In the United States, the use of crime mapping began a little later than it did in Europe. Because the United States was a relatively new country in the 1800s, reliable maps were not readily available and census data were not regularly collected, as they were in France and England at that time. The first substantive spatial analysis of crime in the United States was conducted in the 1920s and 1930s by urban sociologists in Chicago. Their crime research and related crime maps linked crime and delinquency to factors such as social disorganization and poverty. In fact, these scholars’ spatial analysis of juvenile delinquency and social conditions in Chicago is considered to be one of the foremost examples of crime mapping in the first half of the 20th century (Groff & La Vigne, 2002). Crime mapping was a theoretical component in the development of the concentric zone model, which contends that in an urban setting different types of zones (areas with different purposes) form around a central business district and that some of these zones are more prone to crime and disorder than are others. Researchers who analyzed the locations and distribution of gangs in Chicago based on the concentric zone concept found that gangs were concentrated in parts of the city where social control was weak and social disorganization was high (Weisburd & McEwen, 1997). Most of the early crime mapping conducted in both Europe and the United States examined aggregate levels of crime by area. However, evidence exists of a map that was created by hand in 1929 by Chicago school researchers in which the home addresses of more than 9,000 delinquents were clustered in particular areas of Chicago (Weisburd & McEwen, 1997). Through the 1950s, 1960s, and 1970s, sociologists and others who were interested in crime and its causes continued to examine the sociological factors associated with crime. The explanations and geographic methods of analysis used remained fairly uncomplicated during this period, possibly owing to the researchers’ focus on sociological factors and the lack of adequate technology (Groff & La Vigne, 2002). In the late 1960s, scholars began conducting spatial analysis of crime with the help of large computer systems and unsophisticated visualization methods (Weisburd & McEwen, 1997). 1970 to Present From the late 1960s through the early 1980s, a group of researchers in England, Canada, and the United States shifted their focus of the study of crime away from what traditional criminology examined—criminal offender—and toward the criminal event and its context, including the physical and social environments that create opportunities for crime (Brantingham & Brantingham, 1981; Clarke 1980, 1983; Cornish & Clarke, 1986). This movement affected crime mapping, as researchers shifted from aggregate analysis of crime and social factors to the analysis of discrete criminal events and their locations (for a more detailed discussion of this theoretical approach, see Chapter 5). Consequently, researchers began to incorporate information about geography and environment into their study of crime problems and related issues, such as rape (LeBeau, 1987) and a host of other crimes (Harries, 1980) as well as distribution of police personnel (Rengert & Wasilchick, 1985). In the early 1980s, client server technology made geographic information systems more available, and this enabled a number of police departments to experiment with crime mapping in their everyday work (Groff & La Vigne, 2002). A project funded by the National Institute of Justice partnered researchers and practitioners in five U.S. cities to use innovative analytic techniques in studying drug markets and tracking their movements over time (Groff & La Vigne, 2002):  In New Jersey, Rutgers University and the Jersey City Police Department implemented an experimental design to test problem-oriented policing responses to reduce violent crime.   In Connecticut, the city of Hartford joined with Abt Associates, a private consulting firm based in Boston, to promote crime mapping as a way of encouraging community involvement in addressing crime problems.  In California, the San Diego Police Department and the Police Executive Research Forum mapped drug incidents and drug markets with police interventions in an experiment that evolved into a crime mapping system.  In Pennsylvania, Carnegie Mellon University and the Pittsburgh Bureau of Police developed a system in which thematic maps were created to show changes in crime by area over time.  In Missouri, the Kansas City Police Department partnered with the Crime Control Institute to develop an innovative narcotics enforcement strategy aimed at reducing the violence and disorder associated with retail drug sales in residential neighborhoods These projects led the way for crime mapping partnerships between practitioners and researchers and demonstrated how communities could use GIS tools as a central part of crime control initiatives. The program was focused primarily on the use of geographic police data, but the participants found that examining other geographically based data contributed to their ability to target problem-solving strategies, brought together key partners with different perspectives, and facilitated the assessment of their joint efforts (Taxman & McEwen, 1997). In the early to mid-1990s, significant improvements in computer technology and police data systems made electronic crime mapping a much more practical tool for police and researchers. GIS software became available for desktop computers as these computers became capable of processing large amounts of data quickly. In addition, police data on crimes, arrests, accidents, and calls for service became available electronically through computer-aided dispatch systems as well as through electronic records management systems (for discussion of these innovations, see Chapter 7) Geographic data such as street and census information became widely available in electronic format and were provided free or at minimal cost by a variety of government agencies and commercial organizations. All of these developments helped to advance the field of crime mapping beyond manual methods and the use of large, costly mainframe mapping systems. In 1993, the Illinois Criminal Justice Information Authority and the Sociology Department of Loyola University of Chicago joined forces to present a computer crime mapping workshop in Chicago. In a publication resulting from the workshop titled Crime Analysis Through Computer Mapping (Block, Dabdoub, & Fregly, 1995), participants—many of whom are top researchers and analysts in the field today— described spatial analytic techniques and offered practical advice for both police professionals interested in implementing computer mapping in their agencies and students of spatial analysis. This workshop was one of the first efforts to bring practitioners and researchers together to discuss crime mapping. During the mid-1990s, the federal government, in a movement spearheaded by Vice President Al Gore, provided increased support for crime mapping technology and methods. Police agencies received federal funding to obtain crime mapping technology, and several programs were developed specifically to assist police agencies with the implementation of crime mapping. The U.S. Department of Justice’s Office of Community Oriented Policing Services (the COPS Office) allocated a significant amount of funding for crime mapping software and equipment through a program called MORE (Making Officer Redeployment Effective). The primary objective of this funding was to “expand the amount of time current law enforcement officers can spend on community policing by funding technology, equipment, and support staff” (Office of Community Oriented Policing Services, 2004). Table 4.1 displays the details of the MORE funding, including how much of the money was allocated directly to crime mapping technology and staff. As the table shows, in a period of only 7 years the COPS Office provided more than $53 million to police agencies specifically for crime mapping To accompany the MORE funding, the COPS Office, in partnership with the Police Foundation, created the Crime Mapping Laboratory in 1997 to assist the policing community in integrating crime analysis and crime mapping into community policing and problem solving. Over the years, the lab has provided a wide range of training opportunities and technical assistance to the policing community and has published numerous reports and resource documents (updated yearly) on topics related to crime analysis, mapping, and problem solving. Its most recognized product is thenewsletter Crime Mapping News (“Police Foundation Crime Mapping Laboratory,” 2003, p. 1) The Crime Mapping Research Center, now called the Mapping and Analysis for Public Safety (MAPS) program, was formed within the Department of Justice’s National Institute of Justice in 1997 with the goal “to promote research, evaluation, development, and dissemination of GIS technology for criminal justice research and practice.” The program provides “many beneficial services such as grant funding, annual conferences, information on training centers, publications, research, and more” (Mapping and Analysis for Public Safety, 2004). Since its creation, the MAPS program has held annual conferences at which practitioners and researchers come together to discuss research and spatial analytic techniques. The program has also conducted a national survey of crime mapping, funded fellowships, developed training curricula, and published books on crime mapping. With the program’s help, the United States has seen interest in and development of crime mapping and crime analysis techniques increase significantly among police departments and researchers. In 1998, the National Institute of Justice created the Crime Mapping and Analysis Program (CMAP), the mission of which is “to provide technical assistance and introductory and advanced training to local and state agencies in the areas of crime and intelligence analysis and geographic information systems (GIS). GIS include crime mapping, global positioning systems, automatic vehicle locator systems, and the use of this technology for the electronic home monitoring of community corrections clientele” (Crime Mapping and Analysis Program, 2004). CMAP has provided training to a significant number of crime analysts and officers in the field. In 2001, CMAP held a symposium on crime mapping topics that resulted in a publication titled Advanced Crime Mapping Topics (Bair, Boba, Fritz, Helms, & Hick, 2002), a collaborative document written by the attendees that includes articles on the role of crime mapping in crime series or investigative analysis, in operations research or resource allocation studies, in problem solving or applied research, and in discrete site analysis. Another relatively recent influence on the use of crime mapping in policing is Compstat, a data- and mapping-driven police management strategy created by the New York City Police Department and adopted by other police agencies across the United States. A core component of Compstat is police officials’ use of crime mapping software and analysis in weekly meetings to understand local patterns of crime and disorder incidents. Crime mapping is such an integral part of the Compstat program that during the 2001 television season, CBS’s The District, a show based on New York’s Compstat experience, highlighted crime mapping in every episode (Theodore, 2001). To date, no historical study has been conducted on the adoption of crime mapping by police agencies, but David Weisburd, a distinguished professor in the field of crime and place, recently examined the rate of adoption of crime mapping in the 1990s through a number of surveys and a pilot study of his own and found that “crime mapping has become widely diffused among police agencies, that the diffusion process began in the late 1980s–early 1990s and gained momentum in the mid 1990s, and that the adoption of crime mapping appears to follow the standards curve of diffusion of innovation” (Weisburd & Lum, 2001, p. 7). Theories Relating to Crime Mapping Rational Choice Rational choice theory is based on classical ideas that originated in the 1700s, with the work of Cesare Beccaria and others who took a utilitarian view of crime (Beccaria, 1764). This perspective suggests that criminals think rationally and make calculated decisions, weighing costs and risks of committing a crime against potential benefits while being constrained by time, cognitive ability and information available resulting in a ‘limited’ rather than ‘normal’ rationality (Cornish and Clarke, 1986). In this sense, rational choice theory also brings in economic ideas and theories into criminology. Routine Activities Routine activities theory helps explain why crime occurs at particular places and times. The theory suggests that crime opportunities are a function of three factors that converge in time and place, including a motivated offender, suitable target or victim, and lack of a capable guardian (Cohen and Felson, 1979). A fourth aspect of routine activities theory, suggested by John Eck, is place management. Rental property managers are one example of place managers (Eck and Wartell, 1997). They have the ability to take nuisance abatement and other measures to influence behavior at particular places. Criminals choose or find their targets within context of their routine activities, such as traveling to and from work, or other activities such as shopping, and tend not to go that far out of their way to commit crimes (Felson, 1994). Crime Pattern Crime pattern theory looks at the opportunities for crime within context of geographic space, and makes a distinction between crime events and criminality, that is, the propensity to commit crime (Brantingham and Brantingham, 1981). Crime pattern theory integrates rational choice and routine activities theories, with a geographic framework, place. The theory works at various geographic scales, from the macro-level with spatial aggregation at the census tract or other level, to the micro-scale with focus on specific crime events and places. Crime pattern theory focuses on situations or places where there is lack of social control or guardianship over either the suspect or victim, combined with a concentration of targets. For example, a suburban neighborhood can become a hot spot for burglaries because some homes have inadequate protection and nobody home to guard the property. Social Disorganization Social disorganization theory emphasizes the importance of social controls in neighborhoods on controlling behavior, particularly for individuals with low self-control or a propensity to commit crime. Social controls can include family, as well as neighborhood institutions such as schools and religious places. When identifying places with social disorganization, the focus is on ability of local residents to control social deviancy (Bursik and Grasmick, 1993). Important factors include poverty, as well as turnover of residents and outmigration, which hinder the development of social networks and neighborhood institutions that lead to collective efficacy (Sampson, Raudenbush, and Earls, 1997) TYPES OF CRIME ANALYSIS ( BOBA,2001) The following are five types of analysis that fall under the umbrella of crime analysis. As you will see, each contains characteristics of crime analysis in general, but each is specific in the type of data and analysis used as well as in its purpose. Intelligence Analysis The study of “organized” criminal activity, whether or not it is reported to law enforcement, to assist investigative personnel in linking people, events, and property. The purpose of intelligence analysis is to assist sworn personnel in the identification of networks and apprehension of individuals to subsequently prevent criminal activity. A related goal is to link information together, prioritize information, identify relationships, and identify areas for further investigation by putting the analysis in a framework that is easy to understand. Much of the information analyzed in the field of intelligence analysis is not reported to the police by citizens but is gathered by law enforcement. Examples of data collection methods include surveillance, informants, and participant observation. In addition, the type of information is not limited to criminal information but can include telephone conversations, travel information, financial/tax information, and family and business relationships. Intelligence analysis has traditionally focused more or less on organized criminal activity, which includes drugs and prostitution syndicates. The data analyzed are plentiful and primarily qualitative, and thus are usually analyzed through qualitative methods. In light of the events of September 11, 2001, intelligence analysis has most recently begun to focus on terrorist activity at the local level as well. Criminal Investigative Analysis The study of serial criminals, victims, and/or crime scenes as well as physical, socio- demographic, psychological, and geographic characteristics to develop patterns that will assist in linking together and solving current serial criminal activity. This type of analysis has also been called “profiling,” which is the process of constructing a “profile” of an unknown offender based on the nature of the crime, the facts of the case, and the characteristics of the victim. As with intelligence analysis, this type of analysis focuses primarily on qualitative data surrounding serious serial crimes such as murder and rape. Data are collected and analyzed on an individual level for those persons primarily or peripherally involved with the incidents. The spatial nature of the incidents and related locations such as the body dump sites or the encounter sites is also considered. The primary purpose of criminal investigative analysis is to develop patterns of serial crimes crossing city, state, and even national boundaries by linking behavior and evidence within and among incidents in order to catch the offender and/or clear cases. This is a very specific type of crime analysis that is primarily done on the federal law enforcement level since these types of crime occur infrequently and cross jurisdictional boundaries and/or clear cases. This is a very specific type of crime analysis that is primarily done on the federal law enforcement level since these types of crime occur infrequently and cross jurisdictional boundaries. Tactical Crime Analysis The study of recent criminal incidents and potential criminal activity by examining characteristics such as how, when, and where the activity has occurred to assist in problem solving by developing patterns and trends, identifying investigative leads/suspects, and clearing cases. Tactical crime analysis focuses on information from recent crimes reported to the police. “Recent” can refer to the last few months or longer periods of time for specific ongoing problems. Tactical crime analysis also focuses on specific information about each crime such as method of entry, point of entry, suspects actions, type of victim, type of weapon used, as well as the date, time, location, and type of location. Field information such as suspicious activity calls for service, criminal trespass warnings, and persons with scars, marks, or tattoos collected by officers is also considered in the analysis. Although quantitative analysis is often conducted once a pattern has been identified, qualitative analysis, (i.e., critical thinking and content analysis) is used to identify patterns and trends initially. Three purposes of tactical crime analysis are 1) linking cases together and identifying the notable characteristics of the patterns and trends, 2) identifying potential suspects of a crime or crime pattern, and 3) clearing cases. The focus of tactical crime analysis is examining data daily in order to identify patterns, trends, and investigative leads for recent criminal and potential criminal activity. Once a crime pattern, suspect, or investigative lead is identified, the information is compiled and disseminated to patrol officers and detectives. Strategic Crime Analysis The study of crime and law enforcement information integrated with socio-demographic and spatial factors to determine long term “patterns” of activity, to assist in problem solving, as well as to research and evaluate responses and procedures. Strategic crime analysis consists primarily of quantitative analysis of aggregate data. Monthly, quarterly, and/or yearly compilations of criminal and non-criminal information such as crime, calls for service, and traffic information are analyzed in aggregate form. That is, general categories such as date, time, location, and type of incident are analyzed instead of qualitative data such as narrative descriptions of incidents. Variables including race, class, sex, income, population, location, and location type are examined along with law enforcement information in the analysis process. The two primary purposes of strategic crime analysis are 1) to assist in the identification and analysis of long-term problems such as drug activity or auto theft and 2) to conduct studies to investigate or evaluate relevant responses and procedures. Both of these purposes correspond very well to the problem solving process (see Section IV for a discussion of crime analysis and problem solving specifically). These types of studies include evaluation of crime prevention programs, in depth examination of a particular crime problem, and implementation of a survey of citizens’ perceptions of crime and the police. They incorporate pre- and postmeasurement as well as both impact and process evaluation methodology. Procedures examined include such activities as deployment and staffing, redistricting of beats or precincts, data entry and integrity, and the reporting process. In sum, strategic crime analysis uses statistical techniques and research methods to investigate long-term problems and evaluate organizational procedures. Analysts who primarily conduct strategic crime analysis are also called problem or research analysts. Administrative Crime Analysis The presentation of interesting findings of crime research and analysis based on legal, political, and practical concerns to inform audiences within law enforcement administration, city government/council, and citizens. Administrative crime analysis is different from the previous types of analysis in that it refers to presentation of findings rather than to statistical analysis or research. The decision of what and how to present information is the primary focus of administrative crime analysis. Often, the type of information that is presented represents the “tip of the iceberg” of all the work and analysis that has previously been done, for example, an executive summary of a report. The purpose and the audience of the information determine “what” is presented along with legal (e.g., privacy and confidentiality), political (e.g., union issues, election concerns), and practical concerns (e.g., complexity of the information presented). The primary purpose of administrative crime analysis is to inform audiences. These audiences may vary from one situation to the next, which is why the type and quantity of information should vary as well. Audiences can be police executives, city council, media, citizens, and neighborhood groups or a combination. An excellent example of administrative crime analysis is the use of the Internet to provide information to the general public. Audiences of a police Internet site include citizens, police personnel, businesses, victims, criminals, and media—essentially everyone; therefore, the type of information published should be appropriate for an array of diverse customers. The information provided should be simple, clear, and concise and should not disclose sensitive information. One rule of thumb would be to only publish information that one would be comfortable seeing on the evening news Crime Analysis Model The following figure displays how all of these types of crime analysis relate to one another in terms of the level of aggregation of the information. That is, types with low levels of aggregation focus on individual cases and used qualitative data and analysis techniques and those with high levels of aggregation focus on a limited scope of larger amounts of data and information. At the top of the figure, criminal investigative analysis and intelligence analysis utilize the least aggregated and most qualitative data. The data consist of information about informal networks of criminals and their non-criminal acquaintances and relatives as well as where individuals live, work, and “play.” The focus here is on the specifics of criminals, the nature of their crimes, their relationships, and their lives in general. Tactical crime analysis utilizes only crimes and activity reported to the police so the data are more aggregate and somewhat less abundant than those used for criminal investigative and intelligence analysis. Tactical crime analysis is primarily qualitative in nature but depending on the data, quantitative techniques can be used to describe characteristics of a given pattern such as the most common time the crimes occur (time series) or where the crimes are located in relationship to one another. Strategic crime analysis utilizes large amounts of data that are even more aggregated than tactical and investigative data. For example, information used in tactical crime analysis is primarily made up of crime incidents but includes such information as date, time, location, methods of the crime, and detailed description of the crime. Strategic crime analysis focuses only on those variables that can be easily quantified, such as date, time, location, type of location, type of crime, and priority. Thus, the type of analysis is more quantitative and the large amount of data calls for statistical operations instead of reading and examining each case individually.  Finally, administrative crime analysis in this figure is literally the “tip” of the triangle in level of aggregation. The focus is presenting the most aggregate or summary information to a variety of audiences. Overall, these types of analysis fall under the general definition of crime analysis in that each one contains some of the key components of crime analysis. For the purposes of the rest of this report, we will focus on examples of the last three types of analysis, tactical, strategic, and administrative, as they are the types of analysis that are most likely to be conducted on a regular basis by a crime analyst in an average law enforcement agency. TYPES OF CRIME MAPPING Single-Symbol Mapping In single-symbol maps, individual, uniform symbols represent features such as the locations of stores, roads, or states. Figure 4.5 is an example of a singlesymbol map showing school locations and streets. An important thing to keep in mind about single-symbol maps is that a GIS places all points on such a map that share the same address directly on top of one another, making it impossible for the map to show how many points there really are. For example, in the map shown in Figure 4.5, if a middle school and elementary school share the same address, the GIS will have placed two gray circles in the same spot, so there is no way someone looking at the map can see all the schools in the area. This drawback of single-symbol mapping is particularly relevant for the mapping of crime and other police data, because crime and other police-related incidents often occur repeatedly at particular locations. Because of this, crime analysts use single-symbol mapping primarily to display geographic information in which there is no overlap; they employ other types of maps to convey information about multiple incidents at particular locations. In addition, single-symbol maps are not useful when analysts are dealing with large amounts of data. Imagine the map in Figure 4.5 with the locations of 100 schools marked. The points would overlap, and the map would be difficult to read. Thus analysts use single-symbol maps primarily when they are working with relatively small amounts of data that do not overlap. Police agencies also often use single-symbol maps to communicate the locations of crimes within patterns to police personnel. Buffers A buffer is a specified area around a feature on a map. Buffers can be set at small distances, such as 50 feet, or larger distances, such as 500 miles, depending on the purpose and scale of the map. Buffers help in crime analysis by illustrating the relative distances between features on a map. The example map in Figure 4.6 shows a park (polygon feature) with a 500-foot buffer, which could be used to show whether drug arrests were made within 500 feet of the park. Buffers can also be used as polygons for data aggregation and comparison. Figure 4.7 shows two buffers (500 feet and 1000 feet) around nightclubs (point features), which analysts could use to compare incidents directly around the nightclubs to those farther out to see whether the activity has a spillover effect on surrounding neighborhoods. Graduated Mapping Crime analysts often use graduated maps— that is, maps in which different sizes or colors of features represent particular values of variables. Figures 4.8 and 4.9 are general examples of graduated size and graduated color maps, respectively (for discussion of specific techniques for creating these maps, see Chapter 12.) In a graduated size map, the sizes of the symbols used for point and line features reflect their value. As noted above, single-symbol maps are not appropriate for displaying data about crimes that occur at the same locations repeatedly. Analysts use graduated size maps for this purpose, because these maps can account for multiple incidents at the same locations. However, like single-symbol maps, graduated size maps are subject to overlapping points if too many data are analyzed at once. Figure 4.8 is a map in which points are graduated by size according to the numbers of crimes at specific locations. In a graduated color map, the colors of the symbols reflect their values; this kind of mapping can be used with points (in a single-symbol map only),2 lines, and polygons. Figure 4.9 is a map that uses colors to show the total numbers of crimes in particular areas—the lighter shaded areas are those with fewer crimes, and the darker shaded areas are those with more crimes. Chart Mapping Chart mapping allows the crime analyst to display several values within a particular variable at the same time (e.g., variable = crime, values = robbery, assault, and rape). There are two types of chart mapping: pie and bar. In pie chart mapping, the relative percentages (represented by slices of a pie) of values within a variable are displayed. Figure 4.10 is an example of a pie chart map that depicts fights, drugs, weapons, and disorderly conduct incidents at nightclubs. The pies are placed at the locations of all the nightclubs in the area mapped, and the sizes of the pies are graduated to depict the total occupancy capacities of the nightclubs, which provides a relative comparison. Some of the nightclubs represented have had all four types of incidents, whereas others have had only two or three of the four, and the percentages (slices) are based only on the frequencies of the values included (not all types of incidents at all nightclubs). In bar chart mapping, the relative frequencies (represented by bars) of values within variables are displayed. In the example in Figure 4.11, bar charts are placed at the locations of the nightclubs in the area mapped. This figure depicts the same data shown in Figure 4.10, but instead of percentages, the heights of the bars show the frequencies of incidents. Density Mapping In density mapping, analysts use point data to shade surfaces that are not limited to area boundaries (as is the case in graduated color mapping). In their most basic form, density maps are shaded according to the concentration of incidents in particular areas. In the map shown in Figure 4.12, the darker colors represent areas in which the incidents are more concentrated, and the lighter colors represent those in which the incidents are less concentrated. Such maps are used to compare small variations in crime levels from one area to another rather than to compare levels of crime within fixed artificial geographic boundaries, as in area maps.(For more detailed explanation of density mapping, see Chapter 12.) Interactive Crime Mapping Rather than a type of mapping, the term interactive crime mapping refers to simplified geographic information systems made available to novice users over the Internet. Many police departments have interactive Web sites where citizens and police officers can conduct basic crime mapping themselves. These applications typically are not flexible or sophisticated enough to be useful to crime analysts. To illustrate interactive crime mapping, Figures 4.13 and 4.14 depict selected screens found on the East Valley COMPASS (Community Mapping, Planning and Analysis for Safety Strategies) interactive Web site, which is hosted by the Redlands, California, Police Department (http://www.eastvalleycompass.org). Figure 4.13 shows the query screen of this site’s mapping program, which allows the user to choose a particular type of data. In other queries, the user can request data for particular locations, areas of interest, or time frames. Figure 4.14 shows the single-symbol map resulting from a query, with its legend on the right-hand side and different types of functions (e.g., zoom, pan, identify) listed on the left. The user can manipulate the map with limited functions, query different data, and print maps and reports