Volume 3 Issue 1 | October 2011

Public Safety

Geography

A Quarterly Bulletin of Applied Geography for the Study of Crime & Public Safety

A Message from the COPS 

Office Director

The Office of Community Oriented Policing Services is excited to bring you Volume 3 of 

Geography and Public Safety. In partnership with the National Institute of Justice, we will 

continue to develop this informative newsletter and publish it quarterly. 

Within each issue, you will find illustrative examples of geographic information systems 

(GIS) in practice. The use of GIS can assist agencies in strategically applying their limited 

resources to make our streets safer and to enhance community policing efforts. We want to 

continue bringing you informative articles that contribute to our understanding of crime 

and public safety, articles that will include new concepts as well as those you have come to 

know. We will also continue providing technical tips, a synopsis of geography in the news, 

and listings of upcoming events.

We have planned a productive year ahead of us, identifying various topics that will be 

covered in future issues. In addition, each issue will focus on a theme, spotlight new and 

innovative research in the field of GIS, and include interviews with leading practitioners. 

We encourage you to use each issue to enhance public safety in your communities.

The theme for this issue is using GIS to address the full spectrum of public safety issues 

facing law enforcement. While mapping crime must remain a key focus, using the power 

of geographic analysis to enhance community policing and problem-solving strategies must 

also be pursued. In this new economy, in which we are all asked to do more with less, it is 

imperative that agencies make informed decisions by making the best use of available data. 

Just as GIS can be used to assess crime incidents, it can also be used to explore issues such as 

community participation, equitable distribution of police services, and procedural justice.

We want to thank the leadership of the National Institute of Justice for their partnership 

and support in this endeavor. Without their ideas and commitment, this publication would 

not have come to fruition. We will continue our partnership in developing future volumes 

of this newsletter. 

I strongly encourage you to visit our website at www.cops.usdoj.gov and view previous issues. 

You can also register at www.cops.usdoj.gov/Default.asp?Item=2567 to be included on the 

subscribers list so you don’t miss an issue. I also encourage you to reach out to our editorial 

staff to discuss your ideas and submissions to this publication.

Bernard Melekian

Director, Office of Community Oriented Policing Services

U.S. Department of Justice

Contents

1 A Message from the COPS 

Office Director

2 Full Spectrum Use of GIS 

by Law Enforcement: It's 

Not Just About Mapping 

Crime

5 Integration of Centralized 

Intelligence with 

Geographic Information 

Systems: A Countywide 

Initiative

8 Engaging the Community: 

Operation Heat Wave

10 Measuring Potential 

Diffusion of Benefits 

and Crime Displacement 

Near Public Surveillance 

Systems

14 Shawnee Viewer: 

Streamlining Police 

Databases 

16 Technical Tips

18 News Briefs

19 Crime Mapping Events
22

G&PS | October 2011

Full Spectrum Use of GIS by Law Enforcement: 

It’s Not Just About Mapping Crime

John Markovic and Nicole Scalisi

Senior Social Science Analysts

U.S. Department of Justice, Office of Community Oriented Policing Services, Washington, DC

An increasing number of law enforcement agencies have benefited from crime 

mapping as geographic information systems 

(GIS)—the hardware, software, and personnel 

for mapping—have become more powerful, 

affordable, accessible, and user friendly. As 

valuable and important as mapping crime is, 

approximately 70% of demands for police 

services are for non-criminal matters. These 

non-crime-related services range from traffic 

control, to finding lost children or elderly 

residents suffering from Alzheimer’s disease, 

to enhanced surveillance for protecting critical 

infrastructure in a post 9/11 era. 

While GIS has been used effectively to 

accomplish tasks such as these, such nontraditional applications of GIS do not receive 

the same level of attention as efforts devoted 

to mapping crime. Particularly in these fiscally 

challenging times when police are being called 

upon to do more with less, departments should 

strive to use GIS analysis and tools to address, 

assess, and enhance the full spectrum of police 

services and responsibilities.

Given the unique mission of the COPS Office, 

we are eager to promote the use of GIS to 

enhance not only the traditional enforcement 

responsibilities but also the three core 

components of community policing: problemsolving, partnerships, and organizational 

transformation. To do this, we encourage 

greater use of GIS to help assess and increase 

the effectiveness of efforts such as outreach, 

prevention, and neighborhood-based risk and 

capacity assessment, as well as the innovative 

use of GIS to assess and advance commitment 

to police accountability and legitimacy.

In this issue, featured articles address this full 

spectrum approach that not only combine 

traditional crime mapping and crime analysis 

techniques but also incorporate elements of 

community policing. The article “Engaging 

the Community: Operation Heat Wave,” for 

instance, illustrates how Targeted Area Action 

Figure 1. Percentage of respondents who feel the police 

and other local services are successfully dealing with local 

concerns about anti-social behavior and crime issues

© Crown copyright and database rights (2011) Ordnance Survey 100023205.
3

Grids (TAAG)—statistically identified 

distressed areas with high risk of crime—

can be used to direct detectives conducting 

outreach to residents of these distressed 

areas to establish leads. The Urban Institute’s 

article “Measuring Potential Diffusion of 

Benefits and Crime Displacement Near 

Public Surveillance Systems” and the 

Shawnee (Kansas) Police Department’s 

article “Shawnee Viewer,” which provides an 

overview of its GIS tool for integrating and 

viewing data about locations, each illustrate 

how GIS can be used to address traditional 

law enforcement concerns and community 

policing strategies simultaneously. 

For future issues of G&PS, readers are 

encouraged to submit examples, articles, and 

tech tips that reflect geographic approaches 

to the full-spectrum of public safety issues. 

For policing agencies, these efforts should 

encompass both traditional crime mapping 

as well as non-traditional applications of GIS 

related to community policing. In an effort 

to prime the pump, we offer a few examples 

below of what today would be considered 

non-traditional mapping supportive of 

community policing.

Example One: Mapping 

Citizen Perceptions 

and Levels of Satisfaction

Thematic mapping has been used, albeit 

sparingly, to assess and compare residents’ 

perception and levels of satisfaction with 

the police, of public safety issues, and 

about the community. Understanding how 

these dimensions vary by neighborhood 

allows police to assess impacts across the 

neighborhoods they serve and identify 

geographic areas where outreach and public 

relations efforts could be directed.

An illustrative example of this type of citizen 

perception mapping can be seen in Figure 

1, which shows results from the United 

Kingdom’s Place Survey comparing wards 

across the county of Cambridgeshire. For 

this map, the indicator reflects the percent of 

respondents that agree “the police and other 

local services are successfully dealing with 

local concerns about anti-social behaviour 

and crime issues.”1

 Simple visualization of 

variations across wards in maps such as these 

may point to places where police and other 

local agencies may want to devote outreach. 

These maps may also be shared with 

community groups to serve as a foundation 

for discussions with those in communities 

that feel more disaffected. 

Figure 2, which also reflects data from the 

United Kingdom’s Place Survey, shows the 

percentage of respondents who “perceive 

drug use or drug dealing to be a problem 

in their local community.”2 Maps of citizen 

perception regarding levels of public 

disorder can provide an additional indicator 

of where problems may exist. These areas 

may confirm what official crime data 

captured, such as incident reports or arrests, 

but they also may help identify areas where 

crime and disorder are under-reported.

Besides relying on survey data, other types of 

data that could be mapped to assess citizen 

perceptions of police include citizen-initiated 

complaints against police, either as raw 

numbers or normalized against a baseline of 

citizen contacts (e.g., number of complaints 

resulting from traffic stops divided by 

number of traffic stops times 1,000).

Example Two: Mapping 

Police Behavior 

Rather than just mapping crime, police may 

also map locations where they interact with 

the public. Many departments map field 

contacts as well as the locations at which they 

provide services such as “well-being checks.” 

GIS also can be used to assess police activity 

and behavior. Maps can be used to assess 

distribution of activity across geographic units 

while also taking into account contextual data 

that may drive that behavior.

Included within its annual internal affairs 

reports, the Charlotte-Mecklenburg Police 

Department has used density mapping to 

Figure 2. Percentage of respondents who perceive drug use 

or drug dealing to be a problem in their local community

© Crown copyright and database rights (2011) Ordnance Survey 100023205.
44

G&PS | October 2011

assess the degree to which their deployments of 

force are geographically distributed and how 

the density of incidents involving force relates 

to crime hotspots. 

As Figure 3 illustrates, there is considerable 

correspondence between the highest density 

locations for use of force in 2009 and areas 

representing arrest hot spots.3

The utility of such maps concerning 

community relations services is that the strong 

relationship between use of force and crime 

may allay some concerns about the unequal 

distribution of force across neighborhoods. 

Figure 4 shows further utility of this approach 

by comparing changes in use of force compared 

to the previous year.4 At the city level, the rate 

in which use of force was deployed in 2009 

decreased to 1.5 use-of-force incidents per 100 

arrests from 1.7 in 2008. However, when seen 

in a change map, local dynamics are revealed; 

increases and decreases at specific locations are 

clearly depicted. ■

Notes

1 Figures 1 and 2 are accessible on a webpage that 

allows for interactive query and mapping http://

map1.cambridgeshire.gov.uk/observe/Flash/Place%20

Survey%202008/atlas.html. Click the box labeled 

“Data” to change the indicator from the Place Survey to 

be thematically mapped. 

2 ibid. 

3 Figures 3 and 4 are reproduced from the CharlotteMecklenburg Police Department’s 2009 Internal 

Affairs Report: www.charmeck.org/city/charlotte/

CMPD/organization/PoliceChief/InternalAffairs/

Documents/2009IAReport.pdf 

4 ibid.

Figure 4. Charlotte-Mecklenburg Police 

Department’s changes in density of use of force 

relative to arrest hotspots

 

 Appendix 2 

33 Figure 3. Charlotte-Mecklenburg Police 

Department’s density of use of force relative to 

arrest hotspots

 

 Appendix 1 

32
5

Under the cover of winter darkness, a sophisticated crew of disguised 

burglars used acetylene torches and power 

tools to enter commercial buildings and 

cut into automated teller machines (ATMs) 

throughout Morris County, New Jersey. 

Their efforts were highly organized, their 

movements appeared synchronal, and 

their overall proceeds exceeded $100,000. 

One night in March, as this crew gained 

entry into their 15th building, they were 

greeted by a burglary task force, which was 

comprised of law enforcement officers from 

nine different agencies. In the months that 

followed, the suspects pled guilty to all 15 

commercial burglaries and received 8 years 

in state prison for their crimes. 

This scenario isn’t a script from Hollywood; 

it is the result of an investigation that 

concluded in March of 2010 in Morris 

County. Through the centralization of 

intelligence and a strong partnership 

with municipal police departments, law 

enforcement resources are readily shared to 

reduce crime throughout the county. 

Globalization of Crime

Morris County stands in a unique position 

to address the issues of narcotics, gangs, and 

drugs as a suburban problem rather than 

an urban epidemic. With the high density 

of road networks that intersect the county, 

traveling and commuting into Morris 

County from surrounding criminogenic 

urban areas has become easier. These state 

highways, interstates, and the abundance 

of secondary roads have exposed Morris 

County’s residential communities to an 

aggregation of motivated offenders searching 

for potential targets with valuable rewards. 

With the globalization of crime, criminals 

are no longer restricted to geographic 

boundaries. However, offenders still assume 

that police agencies don’t share data. In 

the past, these assumptions would have 

been accurate, but with the proliferation of 

web-based intelligence-sharing databases, 

agencies can easily disseminate data 

and track offenders throughout various 

geographic areas.

Intelligence Crime Task Force

In 2007, Morris County Prosecutor Robert 

A. Bianchi, Esq., created the Morris County 

Prosecutor’s Office Intelligence Crime Task 

Force (ICTF) to meet the newly adopted 

demands of the intelligence-led policing 

(ILP) model. The ICTF’s function is to 

conduct targeted investigations that focus 

on the worst offenders, specifically those 

individuals actively engaged in crimes 

relating to gangs, drugs, weapons, and 

burglaries. 

The ICTF investigative staff is fully 

integrated with specialized assistant 

prosecutors who actively engage with 

the detectives in daily investigations and 

operations. This partnership marries the 

ILP model, practiced by the investigative 

staff, with an aggressive prosecutorial model, 

managed by the legal staff. As an additional 

layer to this hybrid philosophy, the local 

police departments actively contribute and 

are enthralled in this process. Without the 

support and contributions of the 37 local 

municipal police departments, efforts to 

centralize intelligence would be highly 

unsuccessful. 

The Morris County Prosecutor’s Office 

ICTF, as well as the Morris County Sheriff’s 

Office and the Morris County Park Police, 

focus their efforts on centralized resources. 

Centralization includes the collection, 

collaboration, and dissemination of 

resources in a more effective and efficient 

manner.

The ICTF resembles a regional or county 

fusion center, where the goal is to emulate 

a service agency for the municipal 

departments covering the 500 square 

miles of Morris County. In its basic form, 

the municipal departments provide data 

and intelligence from their respective 

jurisdictions to the ICTF. This data is 

compiled into a central database, analyzed, 

and distributed as actionable intelligence to 

the broader Morris County law enforcement 

community. After distributing these 

intelligence products, the law enforcement 

community evaluates the trends and 

investigates persons of interest, or people 

who are actively contributing to these crime 

trends. These investigations are further 

developed using geospatial intelligence.

Standardization of Codes

Before implementing the use of geographic 

information systems (GIS) countywide, 

one of the most fundamental reform 

efforts Prosecutor Bianchi addressed was 

the need to standardize the incident codes 

(CAD/RMS) in an effort to comply with 

the analytic demands of the ILP model. 

By standardizing these codes, data is 

efficiently and uniformly collected in a 

central database that is accessible to every 

department countywide. 

Integration of Centralized Intelligence with Geographic 

Information Systems: A Countywide Initiative

Captain Jeffrey S. Paul and Agent Thomas M. Joiner

Morris County (New Jersey) Prosecutor's Office 
66

G&PS | October 2011

To maximize the productivity of this 

database, a considerable amount of time was 

spent collectively with the municipal chiefs 

evaluating and standardizing the data, so realtime analytics can be applied to investigative 

operations. These changes were made 

prospectively, and the definitions are based 

on a common understanding of specific call 

and crime types (incident codes) within every 

police department. For instance, incident 

codes were categorized into commonly 

accepted groups to measure and forecast 

crime trends more easily and accurately. More 

specifically, instead of measuring overall 

burglary incidents, the standardized codes 

divide burglary into three types: residential, 

commercial, and motor vehicle. 

These incident codes are captured into a 

database and geocoded at the parcel level in 

Esri ArcGIS 10.0 as a separate crime layer. Data 

from this layer is complemented with additional 

layers including parole releases; residential, 

employment, and leisure activity spaces of 

chronic offenders; prior incidents; and weekly 

transactions from pawn shops throughout 

Morris County and surrounding counties. 

Operational Analysis

Prosecutor Bianchi’s strategic goal is to 

reduce overall crime countywide without 

requiring additional resources. To achieve 

this, the standardized crime data is analyzed, 

and problematic areas are identified. After 

classifying an area as high risk or problematic, 

agencies are deployed to these areas to 

suppress the emerging crime problem, placing 

particular concern on eliminating the problem 

rather than diffusing or displacing it. 

The use of GIS has simplified the process 

of determining which areas are identified. 

For instance, monthly or bi-monthly 

burglary reports are distributed and include 

descriptive maps of overall patterns and 

emerging trends; hot spot analysis; crime 

forecast models such as Risk Terrain 

Modeling or Journey to Crime Analysis; 

profiles of arrested individuals, including 

target selection locations and Modus 

Operandi; temporal trends; and monthly 

comparisons of incidents. These reports 

are generated based on the aforementioned 

standardized data and intelligence submitted 

by the municipal departments. 

Share your agency’s GIS efforts and research stories by 

e-mailing Jessica Mansourian at jessica.mansourian@usdoj.gov

Subscribe free-of-charge today by visiting 

www.cops.usdoj.gov/Default.asp?Item=2567

G&PS is published by the Office of Community Oriented Policing Services (the COPS Office)

Feature in the next issue of
7

The forecasts, which adopt the techniques of 

Risk Terrain Modeling, utilize past criminal 

events, as well as variables that are correlated 

with burglary incidents, to create risk scores 

for small geographic areas throughout Morris 

County. These risk values, or high-risk scores, 

represent areas that are geographically and 

statistically similar to areas that have been 

victimized in the past. For the analysis, five 

significant variables are used to create and 

forecast high-risk areas: (1) past burglaries, 

(2) the residential location of individuals 

arrested for theft or burglary between 2009 

and 2011, (3) the proximity to major 

highways, (4) the geographic concentration 

of males between the ages of 16 and 24, and 

(5) the location of apartment complexes 

and hotels. By operationalizing the spatial 

influences throughout the county, agencies 

allocate resources to these identified areas in 

a proactive manner.

Tactical Analysis

Once specific crime patterns are identified, 

short-term operations are coordinated 

to apprehend the targeted offenders. 

One specific technique used to aid an 

investigation is geographic profiling. 

Together with ArcGIS, geographic profiling 

gives the ICTF the ability to use heuristic 

algorithms to delineate specific regions that 

have higher probabilities of containing an 

offender’s residence, place of employment, 

or leisure space. From these probabilities, 

we prioritize these areas and develop a list 

of likely suspects based on the GIS data that 

falls within our search radius. 

Rather than use a calibrated distance decay 

function, the Morris County Prosecutor’s 

Office combines the truncated negative 

exponential distance decay function with 

a weighted land usage variable. This land 

usage variable is an ordinal level variable 

consisting of different classifications. By 

examining the last known address of prior 

offenders, the land use classifications are 

assigned a value based on the frequency 

or prior likelihood that they contained an 

offender’s residence. These weighted values 

are factored into the geographic profiling 

calculation to produce more accurate results; 

this modified calculation takes into account 

the road networks, lakes and ponds, and 

diverse land use. These estimates, combined 

with the additional data, have led to 

successful results, as stated previously with 

the apprehension of the “ATM Bandits” in 

March of 2010.

Conclusion

While the obvious benefit of centralization 

is the significant reduction of crime, an 

added benefit is that the reduction of 

crime comes at no additional cost to any 

police agency. Instead of spending money 

to reduce crime, agencies share data and 

resources and periodically allocate officers to 

areas that have been identified as emerging 

or problematic. Inter-agency officer 

allocation is strictly voluntary and on an 

as-needed basis. By lending an officer to 

another jurisdiction for a shift, the necessary 

manpower is met and intelligence is shared 

more readily. 

This proactive approach has led to 

successful results in Morris County. 

Since 2007, the total crime index in the 

county has decreased by 11%, violent 

crime by 21%, and property crime by 

7%. These results support the shift from 

quantitative result to qualitative results. 

Under Prosecutor Bianchi’s initiative, 

there have been roughly 1,000 more years 

of state prison sentences handed out 

with fewer cases having been filed. These 

numbers represent the problematic or 

chronic offenders who are receiving longer 

state prison sentences, and yet those most 

problematic offenders in need of social 

services continue to receive rehabilitation 

efforts. Qualifying low-risk offenders are 

admitted into the new Mental Health 

Diversionary Program, which Prosecutor 

Bianchi also implemented. 

With shrinking budgets and a constant 

demand for services, the law enforcement 

community must find a way to provide 

citizens with services in the most cost-efficient and effective manner. By centralizing 

intelligence, using proactive measures, and 

adopting an analytical presence, agencies 

can target prolific offenders to reduce crime 

in the community. With the assistance of 

geographic information systems and the 

centralization of intelligence, the spatial 

boundaries of police departments become 

limitless and the demands of the taxpayers 

are fulfilled. ■
88

G&PS | October 2011

Operation Heat Wave is a summer crime reduction initiative launched by the Dallas 

Police Department with the intent of reducing 

overall citywide crime by focusing specifically 

on residential and business burglaries, other 

thefts, and motor vehicle burglaries. The initiative builds upon the coordinated efforts that 

occurred last year during the summer crime 

initiative, Operation Triangle. This year there 

is a two-pronged approach that, first, allocates 

resources where they would have the most effect 

in preventing offenses and, second, attempts 

to engage the community in crime-fighting 

efforts through the use of door-to-door contacts 

soliciting actionable intelligence. 

The initiative is coordinated by Deputy Chief 

Brigitte Gassaway, commander of the Property 

Crimes Division. The initiative first targeted 

one Targeted Area Action Grids (TAAG) area 

in each of the seven patrol divisions. Beginning 

April 18, 2011, the Dallas Police Department 

has expanded to ten TAAGs to address crime in 

the two categories identified above. 

TAAG areas are geographic hot spots within the 

city where conditions are favorable for crime to 

occur. Twenty-seven areas have been identified 

and represent approximately 7% of the city, or 

about 26 square miles, and have about 30% of 

the total Part I crimes. The model uses a multivariate method that improves the forecasting 

effectiveness of geographic information systems 

(GIS) compared to conventional or retrospective 

mapping methods because it looks at more than 

just crime. The variables or indicators themselves do not create crime; they simply point to 

locations where, if the conditions are right, the 

likelihood of victimization and criminal behavior increases. The TAAG areas produced will 

assist in strategic decision making and tactical 

action by showing where conditions are favorable for crime to occur in the future. 

To create grids, the crime analysis team collects 

data from the event- and place-based indicators. There are 6,838 grids used within the city 

proper, measuring 1,320 feet by 1,320 feet. Using the Esri ArcView GIS program, the analyst 

overlays a continuous one-sixteenth square mile 

grid on the city, and the grids are then spatially 

joined with the data. This results in five separate 

layers with counts per grid. A composite map 

Figure 1. 2011 TAAG areas map prepared by the 

Crime Analysis Unit

Engaging the Community: Operation Heat Wave

Deputy Chief Brigitte Gassaway 

Property Crimes Division, Dallas Police Department

Sergeant Steven Armon

Crime Analysis Unit, Dallas Police Department

Dana Perez

Planning Unit, Dallas Police Department

Legend

TAAG2011

Major Streets

Divisions
9

with aggregated grid counts is produced by 

merging the multiple indicators together. 

The map is displayed in a choropleth, using 

standard deviational classifications and onequarter standard deviation for the interval 

size. Figures 2 and 3 demonstrate the types 

of maps that are used first to identify the 

TAAG area and then to divide the sections 

into areas that a squad can canvas in either 

a 4-hour period on a weekday or during an 

8-hour period on a Saturday. 

The following are the indicators that were 

used to identify problematic areas in the map:

Event-Based Indicators

 Arrests: Drug, prostitution, and 

weapons

 Calls: Shootings, cuttings, drug 

house, prostitution, random gunfire, 

prowler, suspicious person, panhandler, 

in-progress calls; to include major 

disturbances and other calls that 

mention guns, drugs, fighting and gangs

 Offenses: 

» Part 1 Violent Crime—murder, 

rape, aggravated assault, and robbery

» Part 1 Property Crime—burglary, 

BMV, other theft, UUMV...

*not including shoplifting

Place-Based Indicators

 Gang members’ home addresses

 Arrestees: burglary, robbery, and BMV 

home addresses

 Parolee home addresses

What makes this crime-fighting technique 

unique is the community engagement aspect 

where all detectives within the department 

are required to wear their uniforms and go 

out into the community to meet the public 

in these distressed areas. Each detective 

goes into the field at least 32 to 40 hours 

during the summer. There are generally 

150 detectives and administrative personnel 

canvassing during each operation. Each team 

of detectives is assigned to a sergeant and 

is responsible for canvassing a number of 

doors. The detectives go door to door in the 

identified areas to try to obtain information 

on no-lead offenses and other intelligence 

information that could be shared throughout 

the city. 

The belief is that engaging the citizens 

during this brief contact will have a positive 

impact on community relations regardless 

of the amount of actionable intelligence 

that is developed. Detectives also provide 

information on Operation ID; the Lock, 

Take & Hide program; iWatch Dallas; and 

other crime prevention strategies. Detectives 

encourage the citizens to attend crime watch 

meetings and provide information regarding 

an upcoming crime watch meeting in their 

neighborhood. During the months of June, 

July, and August, the number of interviews 

with the citizens increased. 

Dallas Police Chief David O. Brown’s 

philosophy regarding increased community 

engagement is being implemented as 

officers connect with citizens to determine 

information about criminal activity and 

perception of crime in their neighborhood. 

The department believes engaging citizens 

will be a key strategy in holding the line 

on crime. ■

Figure 2. TAAG area identified in the Forest 

Audelia section of Dallas 

Figure 3. TAAG area identified in the Forest 

Audelia section of Dallas with mapped 

community resources

Legend

Commercial

Multi-family

Residential

dpd.SDE.TAAG2011 

selection

Legend

Childcare

Church

Hospital

RecCenters

School

CW/HOA
1010

G&PS | October 2011

Measuring Potential Diffusion of Benefits 

and Crime Displacement Near Public 

Surveillance Systems

Samantha S. Lowry and Nancy G. La Vigne

The Urban Institute

Law enforcement agencies across the country are investing in public surveillance systems to 

assist with crime prevention and police investigations. However, critics question whether cameras simply displace crime to neighboring areas 

that are not under surveillance and, counter to 

those critics, theory posits that crime reductions 

due to cameras may extend beyond their viewing area—known as a “diffusion of benefits.” 

This article describes The Urban Institute’s 

evaluation of the use of public surveillance 

cameras in three cities—Baltimore, Maryland; 

Chicago, Illinois; and Washington, D.C.1

, with 

a specific focus on how geographic information 

systems (GIS) and spatial analyses were used to 

measure potential diffusion and displacement 

effects in the areas adjacent to the camera locations. The area highlighted below, Humboldt 

Park, Chicago, had significant reductions in 

crime following camera installation and, therefore, was a good candidate for investigating 

potential diffusion and displacement effects.

The spatial techniques employed to explore 

the degree to which camera impacts extended 

beyond the cameras’ viewsheds and into the 

surrounding areas were (1) the production of 

density maps of crime concentrations and calculation of Mean Center before and after camera implementation, (2) the use of the weighted 

displacement quotient (WDQ), and (3) the 

use of difference-in-differences (DiD) analyses, 

which enable the determination of whether 

changes found in the previously mentioned 

techniques were statistically significant.

Figure 1. Camera viewshed and buffer development
11

Development of Diffusion 

and Displacement Zones

To provide spatial context for the density 

maps and more rigorous WDQ and DiD 

analyses described later, three specific 

geographic zones for potential diffusion and 

displacement following the introduction 

of surveillance cameras were established 

surrounding the camera sites. The 

immediate vicinity of each of the camera 

areas was defined as extending within 200 

feet of the physical location of the cameras. 

Then 500- and 1000-foot buffers were 

designated around each camera target area 

using two concentric circles around the 

200-foot buffer to look for diffusion and 

displacement effects, respectively (refer to 

the two outer rings in Figure 1). 

Density Mapping and Shifts 

in the Spatial Mean

The first set of spatial techniques employed 

to identify diffusion and displacement, 

density mapping, and the generation of 

spatial means is the most visually persuasive 

yet the least analytically rigorous. Kernel 

density maps, which aggregate and smooth 

out crime to depict concentrations, were 

generated in the areas covered by and surrounding the cameras. 

These maps were generated for all aggregated crime at two points in time—one year 

before and one year after camera installation. For this analysis, the buffer zones 

surrounding the camera areas are used as 

boundaries to examine where the crime 

shifts but do not restrict the movement of 

the data within and outside them. The mean 

center of crime, which depicts the location 

where, on average, crime incidents occurred, 

was then calculated within a half mile of 

each camera target area for the same two 

points in time. Examining the expansion or 

reduction in the most dense (darkest) crime 

areas between pre- and post-installation 

maps indicates an increase or decrease in 

crime, while examining shifts in the mean 

center pre- and post-camera installation 

provides a visual depiction of the movement 

of crime over time (potential displacement). 

Figure 2. Change in density and mean center of crime: Humboldt Park, Chicago
1212

G&PS | October 2011

As shown in Figure 2, on page 11, the darker 

regions, which indicate the highest crime areas 

in Humboldt Park, Chicago, diminished and 

new hot spots were not revealed, while the 

lower crime areas became more expansive. 

The two hot spots along the southern portion 

of the camera area nearly dissolved, and only a 

single hot spot remained on the northern side. 

The mean center, shown as a cross in Figure 

2, also supported the finding that crime was 

not moving beyond the camera area, with the 

center moving less than a single city block. 

These findings suggest that although crime was 

diminishing in the camera areas, it was not 

geographically shifting. In other words, the 

cameras were not displacing crime; rather, the 

reduction was real.

Weighted Displacement 

Quotient

Another means of examining potential diffusion 

and displacement following surveillance camera 

installation is through calculation of the WDQ, 

which measures changes in crime occurring in 

the target area (A), displacement or diffusion 

zone (B), and comparison area (C) using two 

points in time (pre- and post-implementation).2

The displacement and diffusion zones employed 

in this analysis were created using the 500- 

and 1000-foot buffers described above. Given 

that the WDQ, as it was originally intended, 

accounts for only a single displacement or 

diffusion zone, we calculated two separate 

WDQs—one for the 500-foot buffer and 

another for the 1000-foot buffer—over the 

same period. The WDQ formula is provided 

below:

At0 and At1 are crime levels in the target area at 

times 0 and 1; Bt0 and Bt1 are crime levels in 

the diffusion or displacement zone at times 0 

and 1; and Ct0 and Ct1 are crime levels in the 

control area at times 0 and 1.

The quotient is broken into two parts: 

1. The displacement measure, the numerator, 

determines the change in crime in the 

displacement area relative to the change 

in crime in the control area over the same 

period.

2. The success measure, the denominator, 

determines the success of the intervention, 

or the reduction in crime in the target area 

relative to the control area over the same 

period. 

A negative success measure confirms that there 

was in fact a decrease in crime in the target area 

and, therefore, displacement or diffusion effects 

may be occurring and further interpretation 

of the WDQ is needed. A positive value shows 

that crime increased in the target area, and 

the WDQ should not be interpreted because 

displacement of crime would not theoretically 

be expected if crime did not decrease in the 

target area.

There are two general steps involved with 

interpretation of the overall WDQ value: 

determining if the value is positive or negative 

and whether it is greater or less than 1/-1. A 

positive WDQ indicates a diffusion of benefits 

to the specified displacement or diffusion area 

(B), which in this case is either the 500- or 

1000-foot zone, suggesting that crime has also 

declined in the buffer area as a result of the 

intervention. A negative result would suggest 

displacement of crime, with crime in the 

specified zone increasing over the same period. 

Values between 0 and 1/-1 indicate that the 

effect in the buffer zone is less than the effect 

that occurred in the target area. Values greater 
13

than 1 or less than -1 indicate that the 

effects on crime—positive and negative, 

respectively—in the buffer were greater 

than the effects in the target area. 

WDQ results indicated that crime decreased 

in the target area compared to the control 

area, with some crime reduction benefit 

extending to both 500- and 1000-foot buffers in the first 12 months but with no signs 

of displacement.

Difference-in-Differences

While the results from the above methods 

are promising, they lack statistical tests for 

significant change and, therefore, can be 

employed only to suggest whether diffusion 

and displacement may be occurring rather 

than to conclude so definitively. Thus we 

employed DiD analysis, which compares 

net change in crime in the target area using 

a control area to subtract other changes 

occurring in a similar location over the same 

evaluation period. 

Employing this method in the target area, 

we determined that crime dropped by approximately 13% per month on average 

in the Chicago’s Humboldt Park following 

camera installation. Given this statistically 

significant reduction in the camera area, 

we further investigated for diffusion and 

displacement using the same technique. 

This resulted in similar findings to the other 

spatial analyses presented above but with a 

higher degree of rigor—crime displacement 

was not evident within the 500- and 1000-

foot zones. 

It is prudent, therefore, to conclude that 

while cameras had an impact on crime in 

their intended spheres of influence, no 

evidence of displacement to nearby areas 

was detected. In addition, more rigorous 

analyses also yielded no evidence of a diffusion of benefits to areas beyond the camera 

viewsheds, contrary to the spatial results.

Conclusion

Overall, the spatial techniques described in 

this article provided a well-rounded picture 

of the movement of crime in the vicinity of 

surveillance cameras. The density maps and 

mean center techniques provided a depiction of how the concentrations changed and 

shifted in and around the camera areas and 

whether hot spots were truly dissolved or if 

they merely moved to a new location several 

blocks away. 

WDQ provided additional rigor through the 

introduction of comparison areas, enabling 

us to determine proportional change for 

each zone. This technique addressed whether 

there were diffusion or displacement effects, but it lacked a statistical significance 

measure. DiD was the most scientifically 

rigorous of the methods used and, while 

not a spatial statistic, nonetheless employed 

spatially designated areas for analysis purposes and generated a statistic to back up 

the findings of no displacement. Together, 

these methods offer persuasive evidence that 

the crime reduction impact of cameras was 

not countered by a displacement of crime to 

other areas. However, the degree to which 

cameras result in a diffusion of benefits 

remains an open question, with conflicting 

findings and the more rigorous test yielding 

no definitive signs of benefits beyond the 

camera viewsheds. ■

Notes

1 La Vigne, Nancy G., Samantha S. Lowry, Joshua A. 

Markman, and Allison M. Dwyer. 2011. Evaluating 

the Use of Public Surveillance Cameras for Crime 

Control and Prevention. Washington, D.C.: U.S. 

Department of Justice, Office of Community 

Oriented Policing Services.

2 Bowers, Kate J., and S. D. Johnson. 2003. 

“Measuring the Geographical Displacement and 

Diffusion of Benefit Effects of Crime Prevention 

Activity.”Journal of Quantitative Criminology

19:275–301.
1414

G&PS | October 2011

Figure 1. Selected address detail

Shawnee Viewer: Streamlining Police Databases 

Susan C. Smith

Crime Analyst, Shawnee (Kansas) Police Department 

I

n Shawnee, Kansas, the police department 

knew they had a number of disparate databases, 

many in different formats. For an officer to find 

information about any given address, he would 

need to run it in several different databases 

(e.g., CAD, RMS, Traffic, Court, and Offender). 

Often valuable information would be missed 

concerning a particular address because officers 

did not know all of the different databases 

available to them. In essence, requiring officers 

to know each database, to log-in to each, and to 

know how to query in each was time consuming, 

inefficient, and burdensome. 

Shawnee Viewer is an easy and fast way to find information the city has on an address. As the user 

types the address, options for a matching address 

appear in a list below (see Figure 1). Once the 

user selects the address of interest, the program 

searches the Shawnee Viewer database for any 

associated records and displays the data in a form 

(see Figure 2). The base information includes 

parcel ownership, land use, value, legal description, ward/precinct, building permits, special 

assessments, parcel ownership change, special use 

permits, service request, and business license. The 

address can also be viewed on a map, or the user 

can select another address viewable on the map 

(see Figure 3). 

Although Shawnee Viewer was originally created 

as a tool for planning and building permit staff, 

the Shawnee Police Department quickly recognized how it could be used to merge and streamline the address-based databases it maintained. 

The department worked with the geographic 

information systems (GIS) division to incorporate most of the available police databases into 

the program. However, the police department 

did not want this data available to all employees 

in the city, so the GIS division created a second 

tab that only police employees can access. This 

police tab includes information such as warrants, 

protection orders, no contact orders, registered 

offenders, suspects, field interview cards, CAD 

events, police reports, and house arrests. 
15

Shawnee Viewer was created using 

Microsoft’s Visual Studio and the Esri 

ArcReader and ArcGIS Publisher, 

so deploying the program, which is 

transferrable to other police departments 

nationwide, is free of charge. Shawnee 

Viewer is loaded on all PCs in the city, and 

SQL Server Express is the database. 

In supporting the community policing 

philosophy of the Shawnee Police 

Department, its Crime Analyst Susan C. 

Smith felt officers, especially patrol officers, 

needed to have as much information 

as possible about any given address. 

Understanding that the GIS department had 

already undergone a massive integration of 

disparate databases, all of which contained 

information about addresses in the city, and 

had created the Shawnee Viewer, Smith 

worked closely with GIS Analyst Doug 

Hemsath to use the information already 

contained in the Shawnee Viewer to integrate 

the police-only databases. 

Having as much information as possible 

about the city’s addresses helps to ensure 

officer and community safety. Information 

from Shawnee Viewer is used to better 

inform the officers who are serious about 

reducing crime and disorder, especially in 

going beyond incident-oriented 911 policing 

that had been done for decades. Rather 

than blindly responding to a given address, 

officers can quickly tap in the destination 

and obtain detailed information about that 

address without having to sign into and 

search a number of separate databases. 

Shawnee Viewer also supports and 

emphasizes personal service to the public, 

as opposed to a bureaucratic response to an 

address. Providing information that a person 

is mentally unstable, disabled, hearingimpaired, or easily confused or disoriented 

to an officer prior to interacting with 

the resident leads to a more appropriate 

response and/or approach at the residence. 

It also helps to ensure that citizens 

(especially those with special circumstances 

like those described above) are treated like 

real people, not numbers, and shows the 

public that the police really do care about 

citizens' well-being.

Finally, use of Shawnee Viewer can lead to 

more positive contacts between the public 

and the police by having the officer be more 

knowledgeable about the people, conditions, 

situations, and environment in the community. It provides specific information for 

police-citizen contact and often information 

needed for criminal investigations and problem solving in the community. The police 

are able to use the information to map areas 

of concern, select criteria for further analysis, 

and make recommendations to officers for 

specific needs at a given address or group of 

addresses. This leads to better, more effective 

policing in the city, as well as a much better 

use of resources. ■

15

Figure 3. Map of selected address

Figure 2. CAD data associated with selected address
1616

G&PS | October 2011

Crime analysts and GIS professionals have a new set of free tools intended to create and 

share map products on the web. ArcGIS.com is 

devoted to cataloging and hosting users’ data 

and is central to a group of new solutions. An 

analyst can post and share data in a variety of 

formats and make this data available for use in 

three hosted environments: ArcGIS Explorer 

Online, ArcGIS for Mobile, and Community 

Analyst. Each of these solutions has useful 

purposes for police departments. This article 

introduces uploading and cataloging data on 

ArcGIS Online and shows how to create an 

online map application that can be shared.

Cataloging Data 

for ArcGIS Online

ArcGIS Online is the center for hosting data 

and managing security for data sharing with 

other users and groups. Initially, users are 

required to create a free account with ArcGIS.

com. Once this user account is created, a 

variety of features are available. Many basemaps 

like Bing aerial photography or USGS quadrants are on hand for quick deployment. The 

Esri Community Basemap incorporates data 

volunteered from many different sources. Cartographic representation of this basemap can 

be modified—e.g., users can set it to clear or 

subdue levels of transparency to give context to 

the crime data that the user brings to the stage. 

Esri keeps some functionality acquirable as 

premium services. How the user shares data 

(and what functionality is available) is dependent on the user’s access to ArcGIS Server and 

the future availability ArcGIS Online premium 

services. Because many analysts do not have 

immediate access to install ArcGIS Server, and 

ArcGIS Server requires complex installation 

and operating instructions, this article focuses 

on two cloud-based resources for storing and 

symbolizing data. 

Uploading Shapefiles 

for Online Maps

Users can upload shapefiles directly into a map 

on ArcGIS Online. This is the only free method 

immediately available for users to create maps 

with (1) ArcGIS Online for a public map, 

(2) ArcGIS Explorer for an online slideshow 

presentation, or (3) the ArcGIS Mobile application. The Esri Community Basemap places 

size limitations on shapefiles so that users can 

upload only zipped shapefiles that are under 

1MB or under 1,000 shapes. This can still be 

an effective size for showing smaller subsets of 

crime data. 

The following steps specify how to upload 

shapefiles in this manner:

Step 1. Create a user account with ArcGIS.com

and log in. 

Step 2. Click on the “Map” tab at the top. 

Step 3. Click the dropdown button “Add > Add 

Layer from File.”

Step 4. Click “Chose File,” and select the zipped 

shapefile of an exported subset of the crime data. 

Harnessing The Cloud—Part 1

Philip D. Mielke

City of Redlands (California)

TECHINCAL TIPS

Figure 1. ArcGIS Online allows quick creation of free online mapping applications.
17

Step 5. Click on the layer for the file of data 

just added to the table of contents, and 

click the check box next to, for example, 

“Residential Burgs.” 

Step 6. Click on the added 

data layer, and select 

“Change Symbols.”

Step 7. Select one of Esri’s 

basic symbols, or reference 

a URL for a suitable icon 

image. Users can make and 

store their own PNGs in 

an online storage method, 

such as Dropbox, or use predefined icons. 

For example, www.emsymbology.org/

Police_CAD-RMS/RMS.html lists available 

icons. Simply right click the icon from the 

browser, select “Copy Image URL,” and 

paste it into the address bar.

Step 8. Control the way end users click 

and access shapefile data fields by selecting 

“Configure Pop-up.” 

Step 9. Repeat for as many layers needed for 

the data product. 

Step 10. Click “Save As.” Enter a title, 

searchable tags, summary, and the folder in 

which to save the data. 

Step 11. Click “Share.” This enables sharing 

options for the online map created. Facebook and Twitter are options for police 

departments that have engaged their citizens 

with social networking, or a simple URL 

can be created for sharing in e-mails or on 

websites. The “Embed in Website” option 

allows the code to be copied and pasted into 

an existing website, and the “Make a Web 

Application” option is advisable only if the 

user has direct access to a web server and 

can configure XML and HTML. 

Uploading Layer Packages 

Users can upload layer packages to ArcGIS 

Online directly from the ArcGIS Desktop 

environment. ArcGIS Online allows 2GB 

of storage for this data, and there are many 

clues that Esri intends to offer premium 

hosting for these data services. Layer 

packages will soon be accessible for ArcGIS 

Online Maps, ArcGIS Explorer, and ArcGIS 

Mobile Maps. Currently, users can utilize 

this desktop environment for online storage 

and access. Once this data is added to the 

premium hosting service, users can add 

searchable information to each data profile.

The following steps specify how to upload 

layer packages in this manner:

Step 1. In ArcGIS 10.x, sign in to ArcGIS 

Online by clicking on “File > ArcGIS 

Online...”

Step 2. Symbolize the data intended for 

uploading. Vector data (points, lines, and 

polygons) or raster data (kernel densities or 

surface) can be uploaded. The layer file also 

requires a description saved under “General” 

under the layer properties. This is how the 

user and group users can search and identify 

information about the origin of that data. 

Step 3. Right click on the layer to upload 

to ArcGIS.com. Select “Create Layer 

Package...” 

Step 4. Select the layers to include, and 

“Upload Packages to My ArcGIS Online 

Account.”

Step 5. Click “Validate.” 

This will determine if the data has the 

required elements to be uploaded or if there 

is a problem with uploading this data. Error 

messages are generally intuitive to follow.

Step 6. Click “Share.” An additional 

“ArcGIS Online Package Details” dialogue 

will appear, and the user should ensure 

that the summary, description, credit 

information, searchable tag information, 

and permissions specifying which group 

users are able to see the data have been 

entered. Additionally, “Everyone” can be 

allowed access to search and view the data. 

Layer packages are superior to shapefiles as a 

method for sharing data on ArcGIS Online. 

Layer packages store layer properties as set 

by the analyst. Symbology is stored, as well 

as label, scale level, and field distinctions. 

Layer packages can also be raster data sets, 

which are a necessity for analysts who 

produce kernel density hotspot analysis 

products. Additionally, Modelbuilder has 

a geoprocessing task that allows automated 

methods of uploading and updating data.

ArcGIS Online Community

While logged into ArcGIS.com, searching for 

different tags and keywords brings up a list of 

existing and cataloged data already accessible. 

Larger entities have the enterprise resources 

available to leverage and share cataloged 

data through ArcGIS Server, so there is a 

trend toward finding country-wide (and 

country-scaled) data. U.S. Census, USGS, 

and USFS all provide many different and 

useful representations of their data. NOAA 

provides real-time weather data services, and 

different aerial photography services are easy 

to find for most regions of the United States. 

This catalog of regularly updated data is still 

in its early stages, but as GIS becomes more 

accessible so will agencies that find a value 

returned by sharing their data.

There is an obvious element of social 

networking borrowed from the current 

trend of Twitter and Facebook. Users 

develop and promote groups that have 

a particular focus on a region or a 

functional need. Data has searchable profile 

information with a contact tied to the other 

end that can ask more questions of that 

data. Comment sections on each data profile 

provide an easy means of communication, 

and group users have built-in security 

privileges to allow access to only certain 

data. ArcGIS Online is becoming a little 

more like an online social network for data 

and the agencies that provide that data. 

What will make it work? Accessibility to 

tools that are available only by putting your 

data in the cloud. 

The next Tech Tips will take a look at three 

useful tools on Esri’s cloud. ArcGIS Explorer 

Online can produce online slideshows that 

are navigable, query-able, and perfect for 

CompStat-style meetings. ArcGIS Mobile 

can allow police and field staff the chance 

to view and edit crime data on an iPhone 

or iPad in the field. Finally, Community 

Analyst provides a complex assortment of 

demographics and community data. These 

three applications are made more valuable 

by enabling the user to use his or her own 

data for orientation and context. ■
1818

G&PS | October 2011

Baltimore PD Uses Xora 

GPS To Enhance Officer 

Safety and Increase 

Community Policing

The Baltimore Police Department is responsible 

for a community of more than 641,000 

citizens and an area of more than 92 square 

miles, which means that at any point 2,000 

sworn officers can be dispersed throughout 

a large area. Baltimore PD has enlisted the 

services of Xora technology as a part of their 

new project called “Side Partner”—a program 

intended to increase the productivity of patrol 

officers when they are away from their cars 

by allowing them to use their smartphones to 

run warrants, check license plate numbers, etc. 

It allows officers to have the tools needed to 

work effectively, without being reliant on the 

technology typically located in their patrol cars. 

This allows officers to interact with citizens on 

the street and become more involved with the 

community. 

Xora’s GPS Field Management System now 

allows dispatchers and command staff to know 

where each officer is located at all times. This 

increases officer safety by enabling dispatchers 

to map the location of an officer quickly if they 

are in need of help. Further, Xora’s technology 

also allows the administration to analyze the 

number of officers deployed to each sector 

and district over time, providing them with 

information about how to best assign officer 

deployment in the future to best address the 

needs of the community. ■

Peabody Police 

Detective Develops 

iPhone App To 

Enhance Police-Citizen 

Communication

Detective Peter Olson of the Peabody 

(Massachusetts) Police Department developed 

a new smartphone application called “My 

Police Department,” which allows local citizens 

to communicate with law enforcement through 

the push of a button. The application, which 

is free to citizens, is a platform for citizens 

to report crime, send tips, and ask questions 

directly to the police agency in their area. 

Citizens are even able to take a picture and 

immediately upload it to the site, enabling 

officers to know the exact location of the 

incident through the phone’s GPS. 

Citizens are often the eyes and ears of the 

street, and this application is a way to bridge 

the gap between the police force and the 

community they serve. The new application 

is a cost-effective way for law enforcement 

agencies to engage their community and utilize 

the information they provide in an efficient 

manner. Participating police departments will 

pay a yearly fee for the service based on the 

population of their jurisdiction. The typical 

price for a medium-sized city of 25,000–75,000 

people is about $600–$700 per year. Twenty 

five communities have already signed up for 

the service, including a number of agencies 

in Massachusetts, as well as in Maine, Texas, 

California, Georgia, and Wisconsin. ■

Fusion Core Solution 

Now Available

Esri and Microsoft announced the launch 

of their new data-sharing tool that allows 

federal, state, local, and tribal agencies to 

collect, analyze, share, and track information 

effectively to help identify and prevent public 

safety threats. At the Esri Homeland Security 

GIS Summit held in San Diego, July 10–13, 

Microsoft announced the availability of Fusion 

Core Solutions (FCS). The tool is designed 

specifically to identify growing threats by 

organized crime, gangs, drug trafficking 

organizations, and potential terrorists. 

The GIS function allows the spatial analysis 

of suspicious activity reports, crime data, 

and other information related to criminal 

threats and allows quicker dissemination of 

information to first responders. For more 

information about FCS, visit www.microsoft.

com/fusion. ■

NEWS BRIEFS
19

Crime Mapping Events

International Association of Crime 

Analysts & Massachusetts Association 

of Crime Analysts 2011 Training 

Conference

September 19–23, 2011

Hyannis, Massachusetts

www.iaca.net/conference.asp

National Institute of Justice Crime 

Mapping Research Conference

October 17–21, 2011

Miami, Florida

www.nij.gov/events/maps/welcome.htm

International Association of Chiefs of 

Police 118th Annual Conference and 

Exposition

October 22–26, 2011

Chicago, Illinois

www.theiacpconference.org/

Association of American Geographers 

Annual Meeting

February 24–28, 2012

New York, New York

www.aag.org
U.S. Department of Justice

Office of Community Oriented Policing Services

145 N St., N.E.

Washington, DC 20530

To obtain details on COPS Office programs, 

call the COPS Office Response Center at 

800.421.6770.

Visit COPS Online at www.cops.usdoj.gov.

COPS Editorial Staff 

Nicole Scalisi

Chief Editor and Senior Social Science Analyst

Office of Community Oriented Policing Services

John Markovic

Senior Social Science Analyst

Office of Community Oriented Policing Services

Jessica Mansourian

Program Analyst

Office of Community Oriented Policing Services

Erin Canning

Senior Technical Editor

Office of Community Oriented Policing Services

Nancy Carlsen

Senior Designer

Office of Community Oriented Policing Services

MAPS Editorial Staff 

Joel Hunt

Social Science Analyst 

National Institute of Justice

Timothy Brown

Research Associate (Contractor)

National Institute of Justice

Visit NIJ Online at www.ojp.usdoj.gov/nij.

The opinions, findings, conclusions, or recommendations contained in this publication are those of 

the authors and do not necessarily represent the official position or policies of the U.S. Department 

of Justice. References to specific agencies, companies, products, or services should not be 

considered an endorsement by the authors or the U.S. Department of Justice. Rather, the references 

are illustrations to supplement discussion of the issues.

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