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STATISTICAL COMMISSION and ECONOMIC COMMISSION FOR EUROPE

Working Paper No. 19 English only

CONFERENCE OF EUROPEAN STATISTICIANS Work Session on Geographical Information Systems (Ottawa, Canada, 5-7 October 1998)

Item 6 of the provisional agenda

THE USE OF GEOGRAPHIC INFORMATION SYSTEMS (GIS) FOR STATE AND LOCAL CRIME ANALYSIS Submitted by the National Institute of Justice, U.S. Department of Justice, Crime Mapping Research Center1

CONTRIBUTED PAPER

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Elizabeth R. Groff and Nancy G. La Vigne

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ABSTRACT Until quite recently, the use of Geographic Information Systems (GIS) for the purpose of mapping crimes in the United States was limited to a small group of geographers with an esoteric knowledge of the mechanics of map digitizing and mainframe computer technology. In recent years, however, the marked reduction in the price of personal computer hardware, along with the availability of comparatively more user-friendly desktop mapping programs, has resulted in numerous efforts in law enforcement agencies across the country. The academic community in the U.S. has also made significant strides in the spatial analysis of crime. This paper will trace the growth of spatial and temporal crime analysis and summarize the current state of the field in the United States. It concludes with an overview of future efforts.

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INTRODUCTION

1. Law enforcement officers and civilian crime analysts have been mapping crime virtually since the time that police agencies were established--through the use of push pins and a paper map. The diffusion of GIS into crime analysis has been a slow process primarily because of cost (both hardware and software) and complexity. In the early 1970’s, technological advancements in computers made automated pin mapping accessible only to the largest and most innovative of police agencies. However, these systems required expensive, high-powered mainframe computers and trained personnel to run them. 2. It was not until the introduction of client server technology in the late 1980’s that GIS became available at a more reasonable cost. At this point, a handful of police departments began to experiment with mapping and Geographic Information System (GIS) programs. These programs automate mapping and allow crime analysts and/or officers to produce crime maps with increased speed. However, true affordability did not arrive until the early and mid 1990’s when personal computers powerful enough to handle large databases were coupled with software programs that did not require the disk space, memory, and processing speed of a mainframe or workstation computer. Since the mid 1990’s, the use of GIS in law enforcement agencies has grown tremendously. 3. During this explosion of activity, United States government agencies have played an increasingly important role in encouraging the use of mapping for crime analysis. Specifically, the National Institute of Justice (NIJ) has actively supported the use of mapping in crime analysis for the last ten years. While most of this support has been in the form of grants to conduct research, recently NIJ established a Crime Mapping Research Center (CMRC). The role of the CMRC is to support research, evaluation, development and dissemination of GIS technology in criminal justice agencies. This paper will discuss the growth of spatial and temporal crime analysis and summarize the current state of the field in the United States. In conclusion, an overview of future efforts will be covered. II. RECENT HISTORY OF CRIME MAPPING 4. Crime mapping was still in its infancy in the 1980s. Only a few departments were using mapping, and in those cases, mapping was often housed in other government agencies (e.g., Planning or Engineering). By the late 1980s, the National Institute of Justice noted the potential of this new mapping technology and established an extramural grant program called the Drug Market Analysis Program (DMAP). DMAP funded partnerships between researchers and police departments in five U.S. sites to use innovative analytic methods to identify drug markets and

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track their movements over time in response to police interventions. These were some of the first crime mapping research projects funded. The results promoted strong and lasting partnerships, and in turn, sparked great interest in GIS among other law enforcement agencies as well as criminal justice researchers (McEwen and Taxman, 1994; Maltz, 1995). 5. Examples of the fruits of these partnerships include those of Rutgers University and the Jersey City Police Department, who together conducted experimental designs testing ProblemOriented Policing tactics to combat violent crime. In Hartford, a partnership between the police and Abt Associates, a private consulting firm, promoted crime mapping as a means of engaging the community in crime prevention efforts. The San Diego Police Department’s partnership with the Police Executive Research Forum to map the incidence and impact of drug markets and police interventions evolved into a system in which crime mapping is fully integrated into the Department’s Problem-Oriented Policing philosophy. And researchers at Carnegie Mellon University, through a partnership with the Pittsburgh Bureau of Police, developed a system whereby thematic maps were produced to illustrate changes in crime by patrol sector over time. 6. Also of note are efforts embarked upon during the same time period as the DMAP project through a partnership between the Illinois Criminal Justice Authority and the Chicago Police Department. This partnership prompted the development of the Spatial and Temporal Analysis of Crime software program, known as STAC. STAC, which operates in conjunction with the MapInfo software program, consists of statistical tools for the identification of “hot spots” of crime and other basic spatial and temporal crime analysis functions.

III.CRIME MAPPING TODAY 7. When discussing the current use of GIS for crime analysis, activities can be divided into current and cutting edge applications. Applications that are currently in use in law enforcement agencies to support crime analysis activities are grouped under the current section. Those applications that are being explored with the goal of expanding the possible uses of GIS and enhancing the theoretical knowledge base are discussed in the cutting edge section. However, these areas are not mutually exclusive. Partnerships between researchers and police agencies are becoming more frequent and are often funded by a national level agency. It is through these academic/practitioner partnerships that the analytic potential of GIS in crime analysis really begins to manifest itself. III.1

Current Uses of Crime Mapping

8. Uses of GIS to support the crime analysis activities in the day to day operations of police departments in the United States are as varied as the departments themselves. Potential uses for the technology are limited only by the imaginations of individuals in the field. This section provides an overview of how law enforcement agencies are using GIS to support a wide variety of activities. GIS is used to: support operations; aid in command and control decisions; assist with investigations; complement community problem oriented policing activities; target crime prevention programs; conduct cross-jurisdictional analysis and enhance collaboration with courts and corrections. The information provided represents a summary of practices in a variety of police departments nationwide. Operations 9. There are several standard types of crime analyses that have proven helpful to patrol officers: automated pin mapping, ‘hot spot’ analysis and radial analysis. Automated pin mapping is the

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most rudimentary and in some ways the most flexible of these. Many law enforcement practitioners have begun to acknowledge the benefits of maps over printouts in enabling officers to visualize patterns in the occurrence of events. Mapping gives them the capability of displaying any time period of events on a map. Not only can the user specify the time period, they can also display events of a certain type or that meet specific criteria. Computer mapping allows one to map several layers of information at the same time, and to signify repeat events at a single address. Further, computerized pin mapping can reveal patterns that are not readily apparent to the naked eye of the line officer on his or her daily beat. In addition, the use of non-crime data from other city agencies (vacant housing or percentage of tenant- versus landlord-owned residences) can be overlaid with crime events to provide a more holistic view of crime in its environment. 10. The ability to map locations of events by their characteristics is an invaluable tool for police officers. Access to this tool is one of the biggest decisions that police departments face when implementing a GIS. Even though desktop mapping programs have become relatively userfriendly, none are simple enough to use without extensive training. Some departments choose to train a few individuals to conduct all spatial analysis. This more centralized method of GIS implementation has the advantage of quicker implementation because it uses GIS software “out of the box” and involves training only a few individuals. Other departments follow a more distributed strategy by giving all officers access to geographic crime analysis. Because computer mapping is just one tool in an officer’s toolbox, it must be easy to learn and easy to use. Thus, the creation of a simplified front-end is required. The development of a computer application is a lengthy process because it requires designing and programming the easy-to-use front end and providing training for all the users. Nevertheless, once implemented a distributed system provides immediate access to all users. Ease of access is one of the pivotal factors in getting officers to use any computer system. 11. The Chicago Police Department was the first law enforcement agency in the United States to place computerized mapping in the hands of line officers. The department designed a front-end system to interface with mapping software that is so user-friendly that it can be used by line officers with little technical expertise. The National Institute of Justice recently funded a similar effort in the New Orleans Police Department, enabling officers to map via a touch screen. These efforts, and others like them, will help extend the utility of crime mapping in that the officers who are witnessing the hot spots on the street, through repeatedly responding to calls-for-service at the same location, will be able to conduct their own analyses and input their own relevant data. 12. GIS is also used to answer the question, Where are the highest concentrations of a crime? Several algorithms are available to calculate the areas of highest density in a point distribution. Many departments use STAC2 or a raster-based density calculation. Once identified, these areas can be targeted for directed patrol activities. Additionally, the community characteristics of the area within the hot spot can be studied to determine why they are hot spots. Another interesting usage of hot spots is to plot hot spots of crimes on the same map with hot spots of specific community characteristics and see where they overlap. One example of displaying related data sets on the same map involves showing violent crime hot spots and hot spots of substandard housing locations. These maps are frequently used to justify requests for help from the local housing authority. Finally, the persistence of hot spots can be examined by plotting several weeks, months or years of hot spots on the same map. This use of hot spots is increasing especially in departments that are instituting results-oriented management. 2

As mentioned earlier in the article, STAC was developed by the Illinois Criminal Justice Information Authority. It is distributed free to interested parties (mostly police departments and researchers). STAC uses a standard deviational ellipse to delineate the highest concentrations of points in a distribution.

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13. Radial analysis is another commonly used GIS function that has important applications in policing. Often police are interested in characterizing the crime situation around a specific location or locations; GIS makes this an easy task. For example, a convenience store is frequently a magnet for criminal activity occurring both in the store and on or near its grounds. An officer may want to illustrate how a particular convenience store had a greater number of crimes committed within 500 feet of it than did other convenience stores in the area. Radial analysis also provides the means for complying with notification laws in the U.S. Many departments, under Megan’s Law, are required to notify residents within a certain distance that a convicted sex offender has moved into a neighborhood. Using a GIS, the departments can plot the address of the registered sex offender and then select all the properties that fall within a specified radius of that location. Letters are then generated to all of the property owners notifying them of the sex offender’s presence. Command and control decisions 14. The ability to keep abreast of crime trends is essential in making informed command decisions. GIS can play an important role at this level. A very recent and successful application of crime mapping to command and control decisions is the New York Police Department’s “COMPSTAT” program. GIS is also used to support major operational endeavors such as parades and presidential visits. 15. News has most likely reached parts outside the United States regarding the success of the New York City Police Department’s (NYPD) comprehensive approach to fighting crime. This approach stems from Wilson and Kelling’s (1982) theory of broken windows, which recommends that police rigorously enforce quality of life violations as a means of preventing more serious crimes from occurring. Police officials applied an additional component to this philosophy through the implementation of a GIS to aid officers in strategic and tactical prevention and control efforts. COMPSTAT, which stands for computerized statistics, is more than a computerized crime mapping program. Rather, mapping is used in conjunction with bi-weekly precinct meetings whereby the precinct commander and his or her team of officers is questioned on the nature of the crime problems in the precinct and how they are responding to them. The department’s GIS is virtually real time, enabling crime analysts to identify crime rashes immediately. When a problem is identified, a meeting is convened during which the precinct commander must explain his or her response to the crime problem. COMPSTAT holds all police officers--from patrol to command level--accountable and responsive to the crime that occurs on their beat. The success of COMPSTAT has prompted other police departments to follow suit, including Baltimore, Washington, DC, and Indianapolis. 16. Less glamorous but still important is the use of GIS to support crowd and traffic management. Careful planning utilizing up to date street information is essential to maintaining smooth operation during traffic diversions. Many times police are called upon to redirect traffic during parades, street festivals and presidential visits. GIS plays a vital role during these situations by providing an accurate street base including pertinent community landmarks. The route or affected areas can be plotted on the map as well as the unit assigned to each traffic diversion point. This makes keeping track of many units in a variety of positions much easier and provides a means of deploying emergency units to areas in response to crowd control or terrorist threats Investigations 17. The use of GIS to support investigations has centered on suspect identification and pattern analysis. GIS can play a significant role in cases in which the victim and perpetrator are

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strangers. These types of cases are particularly frustrating to investigators since they may only have a partial description. However, by linking the location of the crime with databases containing previous offenders, a list of potential suspects can be generated. Examples of databases that may be used to identify potential suspects include: parolees/probationers, arrestees, registered sex offenders, and individuals on pre-trial release. Investigators can utilize any known descriptive factors and a radius around the crime scene to narrow their search. The list that is returned serves as a starting point for the investigators. 18. GIS is also used to examine spatial patterns in the sequence and location of a series of events. This is invaluable when examining events by their different characteristics. For example, a robbery investigator may want to analyze the spatial pattern of armed robberies by time period, day of week, modus operandi and/or victim type. Computer mapping allows the investigator a method to quickly view and compare patterns of crime events. In an enhancement to the techniques listed above, several law enforcement agencies have been working on developing decision support systems capable of ranking potential suspects based on both their similarity to the perpetrator description or MO and their distance from the crime scene. 19. An innovative police agency use of GIS is that of the Baltimore County Police Department (BCPD) in the State of Maryland, which has linked computerized crime mapping with another technological advancement: the auto-dialer, originally developed for telemarketing purposes. Crime analysts use the auto-dialer to broadcast messages of recent crime rashes to specific neighborhoods based on the locations of the crimes. The auto-dialer calls individual households that are identified geographically and issues a recorded message describing the nature of the crime problem, advising residents on appropriate preventive measures, and requesting individuals to report any suspicious behavior. The GIS component of the auto-dialer initiative is used to identify the neighborhood afflicted by the crime problem in such a manner as to flood the vicinity with the recorded advisory, as well as to analyze potential displacement to neighboring areas. The auto-dialer, in conjunction with crime mapping technology, has been credited with apprehending serial burglars, thieves, and robbers throughout the Baltimore County region. Community 20. One area in which maps, especially simple maps, are used extensively is during interactions with the community. Maps provide a forum in which to discuss a neighborhood’s crime problems, both real and perceived. In many jurisdictions, the community expects officers to bring maps with them to the community meetings. This dialogue has the potential to be even more helpful to police; if community members begin to offer information, as well as receive it, the possibilities for empowering neighborhoods are endless. 21. A similar effort, involves a partnership between Abt Associates and the Hartford Police Department to enable community residents to do their own crime mapping in conjunction with the police department’s community policing program. Through an NIJ grant, Abt has developed a user friendly front-end system to accomplish this. 22. Many law enforcement agencies are making their data available on the Internet. This allows citizens the ability to quickly and easily view the crime events that happened in their neighborhood or in the city as a whole. Increased communication is central to community and problem-oriented policing and data sharing is just one part of that communication. Cross-jurisdictional analysis 23. The Baltimore County Police Department is taking the lead on an innovative application of GIS--one that spans multiple jurisdictions. State and local law enforcement in the United States

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consists of over 19,000 law enforcement agencies. Given that each agency operates independently, even the best mapping application in the most innovative police agency is only as good as the jurisdictional boundaries it encompasses. Criminals do not distinguish between jurisdictions, and thus crime is not contained within jurisdictional boundaries. Indeed, prior research suggests that crime occurs in clusters along major thoroughfares (Brantingham and Brantingham, 1984). Because jurisdictional boundaries tend to be drawn along major thoroughfares, the picture of a crime problem is significantly blurred when a crime analyst only has crime data for one side of a street. In response to this common crime analysis dilemma, the Baltimore County Police Department has launched an effort with over a dozen neighboring law enforcement agencies to form a consortium by which the agencies share a common geographically-referenced offense and suspect database. Agencies download crime data to a common database on a daily, or at maximum a weekly basis, depending on the data entry capabilities of the agency, and each agency can map the crime with the mapping software of its preference. This regional consortium has been credited with identifying patterns of auto thefts and recoveries, leading investigators to the location of chop shops, and ultimately to the successful apprehension and prosecution of auto thieves. Collaborations with courts and corrections 24. One of the newest applications of GIS in law enforcement concerns collaboration with courts and corrections. These partnerships usually take the form of data sharing but may also be supportive in nature. For instance, many police departments routinely provide maps as exhibits in court cases. These visual aids have proven effective at helping juries understand chronology and positioning in complex cases. Data sharing arrangements are usually for the purposes of suspect identification or collaboration. 25. In a major demonstration project currently underway at the Department of Justice (DOJ), five cities are using a multi-agency, collaborative approach to problem solving. The project is called Strategic Approaches to Community Safety Initiative and is in the first six months of a two-year effort. Central to this effort is the sharing of data among agencies that include representatives from law enforcement, courts and corrections. In order to facilitate data sharing, a Community Safety Information System is being developed in all five sites. Since GIS is an integral part of the system, participants will be able to analyze data both spatially and tabularly to identify crime problems, analyze the underlying causes of the problem, and assess the impact of their intervention. III.2

Cutting Edge Applications of Crime Mapping

26. This section examines new and exciting projects being conducted that will expand the uses of GIS in crime analysis. Two of the most useful and widespread applications of GIS in the research community are its use to assess the impact of an intervention, and to identify crime patterns for intervention purposes. Assessing interventions 27. There are countless examples of how GIS is being used to assess the impact of law enforcement strategies. The New Orleans police department, for example, is using mapping techniques to examine the impact of the City’s curfew ordinance on both delinquency and violent crimes committed by juveniles against juveniles (Thayer, in progress). Another effort assesses the impact of various strategies to address youth firearms violence and identifies and describes those that are successful and transferable to other jurisdictions. GIS is used as an analytic tool in a number of the ten youth firearm sites (Dunworth, in progress). The San Diego Association of Governments is assessing the effectiveness of using enhanced crime analysis and mapping

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techniques targeted at enforcement and prevention of motor vehicle thefts in the San Diego, California area (Pennell, in progress). 28. GIS is commonly used to assess crime displacement following an intervention. An 18-month study assesses the Oakland, California, Police Department’s Beat Health Unit Initiative, which uses civil remedies for drug and crime abatement, neighborhood improvement, and cooling down of hot spots. Displacement and diffusion effects of the Beat Health program are assessed through the use of GIS (Green Mazerolle, in progress). This project studies the impact of police problemsolving techniques to prevent repeat victimization of residential burglaries. Another example employs a quasi-experimental design to test the effect of interventions that focus on repeat victims in three cities: Dallas, Texas; San Diego, California; and Baltimore, Maryland. Researchers, with police, will analyze burglary patterns and repeat burglaries using GIS to develop an appropriate intervention using the problem solving model and employing situational crime prevention techniques. Trend analysis of reported crime will be used to evaluate the impact of the intervention in the experimental areas relative to the control areas, and GIS will be used to measure displacement and diffusion effects (Stedman et al., in progress). 29. Research in the use of crime mapping is not limited to evaluation and intervention. Academics in recent years have made great strides in refining their analyses through including other mapping related technologies and examining crime on the micro level. These efforts include using orthophotography and Geographic Positioning Systems (GPS) and exploring vertical mapping techniques. Mapping the Z-axis 30. A promising GIS-related technology is the ability to do “vertical mapping”--to plot and analyze an event not just on the x and y axes, but on the z axis as well. Vertical mapping is useful when researchers are analyzing crimes occurring in high-rise apartment buildings, multiple levels of a parking garage, or several stories of a hospital or commercial building. As with the use of orthophotos and GPS, the ability to map and analyze crime on the z axis enables crime analysts to hone-in on the exact location of a ‘hot spot’. Furthermore, this three-dimensional approach offsets the problems associated with counting repeat victimizations by building address, rather than apartment number or even building story or corridor. Crime analysts at the CharlotteMecklenberg, North Carolina, Police Department, partnered with officials of that jurisdiction’s Public Housing Authority, are experimenting with this technique, as is George Rengert and his colleagues at Temple University in Philadelphia. High resolution mapping 31. Orthophotographs are those taken from a bird’s eye view--photos shot from above a landscape. These photos have a fine level of resolution that enables one to identify building “footprints”--the physical shapes of buildings--as well as details such as alleyways and footpaths. Orthophotos provide a more realistic and detailed picture of the environment and can be linked with GIS to enable the analysis of crime at extremely specific locations. 32. A National Institute of Justice grant is currently underway to demonstrate the utility of orthophoto-based GIS for community policing (Harries, in progress). This project will equip patrol officers with GPS devices that, using satellites, can pinpoint the x,y coordinates of exact locations. Thus, given the level of detail of the computerized maps produced by orthophotos and the ability to pinpoint the exact x,y coordinates of incidents, hot spots can be pinpointed to, for example, a specific corner of a playground in a public housing project. Maps generated with this advanced technology may prove more useful to police officers than the digitized maps typically produced with GIS; officers will more easily identify landmarks of places within their beats and

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be better able to communicate with residents about crime problems in their neighborhoods. IV. THE FUTURE OF CRIME MAPPING 33. Now that many law enforcement agencies have adopted crime mapping and have begun to produce the types of tools mentioned previously, they want more. The demand for more sophisticated spatial analytic techniques reflects a user population that knows how they want to use GIS but needs some assistance in making that happen. Not only do law enforcement agencies want more sophisticated analysis tools, they also desire predictive models to help them prevent the next crime. The next sections address these needs in more detail. IV.1

Toward More Sophisticated Spatial Analyses

34. One of the chief complaints of criminal justice researchers and crime analysts studying the spatial distribution of crime is the dearth of statistical tools available in GIS software packages. Indeed, in the area of the geography of crime, little exploration has been made to identify spatial statistics that are applicable to the study of crime and criminal behavior. This is largely a function of the researchers who are studying the geography of crime; most are sociologists and criminologists, and only a very few are geographers by training. While as fields of discipline, sociology and criminology have a strong grounding in statistics, these statistics are limited to cross-sectional, regression, and time-series analyses that do not include a spatial dimension. A strong need exists to branch out to other disciplines, such as epidemiology and geology, to identify statistical tools for spatial analysis: Can we predict the spread of crime the way epidemiologists model the spread of infectious diseases, or geologists model the impact of rainfall on flooding? 35. Once these tools are identified and the algorithms developed, they need to be integrated into existing GIS software packages so that they are user-friendly and do not require the use of multiple analytic programs. IV.2

Creating Predictive Models for Law Enforcement Use

36. In recent years, researchers have made great progress in harnessing the analytic capabilities of GIS to track crime patterns over time and then use this information to create predictive models. Stemming from their initial partnership through NIJ’s DMAP program, researchers at Carnegie Mellon University and the Pittsburgh Bureau of Police are developing an improved early warning system based on artificial neural network technology. This technology is integrated into a GIS, processing spatially referenced data through the trained neural network to create outputs that predict areas that will experience high levels of calls for service for drug crimes (Weisburd and McEwen (eds.), 1997). 37. Given this new micro-level focus, and drawing on the exploratory neural network mapping conducted by Weisburd and McEwen, NIJ is launching a new crime mapping research program. In recent years, crime mapping has emerged as an important tool in law enforcement agencies efforts to scan for problems and assess what are often community/law enforcement collaborative responses to those problems. Ideally, early indicators of troubled areas identify patterns of crimes committed across time and space and inform proactive approached to problem solving. Early warning systems necessitate predictive models that identify hot spots of crime and disorder, as well as areas where crime is abating. NIJ has funded a number of grants to develop such predictive models, drawing on spatial regression analysis, environmental modeling, neural network analysis and other methods, and having the capability of being displayed within a GIS.

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V. CONCLUSION 38. This paper has attempted to provide an overview of the state of crime mapping in the United States and potential future applications of this promising technology. Undoubtedly, the technological advances that led to the diffusion of the innovation of GIS will continue; effectively placing computerized crime mapping in the hands of many more criminal justice researchers and practitioners. However, advancement also requires the exploration of efforts outside of the discipline of criminology, and outside the boundaries of the United States.

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REFERENCES Brantingham, P.J. and P.L Brantingham (1984). Patterns in Crime. New York: Macmillan. Dunworth, T. (In progress). Evaluation of the Youth Firearm Violence Initiative. National Institute of Justice Grant #95-IJ-CX-0069. Green Mazerolle, L. (In progress). Controlling Crime and Disorder Hot Spots Using Civil Remedies. National Institute of Justice Grant #95-IJ-CX-0039. Harries, K. (In progress). Demonstration of Orthophotographic Representation and Analysis. National Institute of Justice Grant #97-LB-VX-K004. Maltz, M.D. (1995). Criminality in Space and Time: Life Course Analysis and the Micro-ecology of Crime. In: John E. Eck and David Weisburd. Crime and Place. Monsey, NY: Willow Tree Press. McEwen and Taxman (1994). Applications of Computer Mapping to Police Operations. Institute for Law and Justice. Grant No. 93-DD-CX-K036. Pennell, S. (In progress). A Coordinated Response to Motor Vehicle Thefts: Evaluation of Enforcement and Crime Prevention Efforts. National Institute of Justice Grant #94-IJ-CX-0027. Stedman, J., Weisel, D., and R. V. Clarke (In progress). Reducing Repeat Victimization of Residential Burglary: A Measure of Police Impact in Three Cities. National Institute of Justice Grant #96-IJ-CX-0042. Thayer, R.E. (In progress). Analysis of Juvenile Curfew in New Orleans. National Institute of Justice Grant #95-IJ-CX-0024. Wilson, James Q. and Kelling, George L.(1982). Broken Windows. Atlantic Monthly, 249(3):29-36 Weisburd, D. and T. McEwen, eds (1997). Crime Mapping and Crime Prevention, part of the Crime Prevention Studies volume 8. Monsey, NY: Criminal Justice Press.