The integration of GIS and GPS
Chapter 6: Crime Mapping Futures

The integration of data and technologies will be pushed to the limit to extract as much value as possible. The possibilities are limited only by our imaginations. Whereas GIS offers a powerful toolbox, GPS, another technology with untapped potential in law enforcement, permits accurate location finding in field settings. Triangulating from 24 satellites (put in orbit at a cost of $12 billion by the U.S. Air Force), GPS, in its more advanced modes, can provide accuracy to one centimeter, or about half an inch. (For a tutorial explaining how GPS works, go to

In reality, however, structural and environmental limitations, such as tall buildings, a forest canopy, or operations in mountainous terrain, and the ability of the Air Force to manipulate the accuracy available to civilians may mean an error of up to 100 meters. These problems can be overcome by using GPS base stations with established locations and manipulations that have come to be referred to as differential positioning GPS or DGPS. This is defined by GPS World Magazine as:

A technique used to improve positioning or navigation accuracy by determining the positioning error at a known location and subsequently incorporating a corrective factor (by real-time transmission of corrections or by postprocessing) into the position calculations of another receiver operating in the same area and simultaneously tracking the same satellites.

The bottom line, however, is that users should generally be prepared for considerably lower resolution than some numbers quoted in promotional materials.

Another possibility for integrating technologies involves the combined use of GIS, GPS, and management information systems (MIS). This would allow close to real-time crime mapping, since the geocoding step would be eliminated (Sorensen, 1997). However, some operational questions need to be examined. For example, with how much certainty will incident locations be reported? A patrol officer may report "arrived" status prematurely, sending what in theory should be the incident location, but what in practice may be erroneous. On the other hand, GPS offers the possibility of accurately reporting places that have no meaningful street address. A shopping mall covering 100 acres may have a conventional street address that is meaningless in terms of conveying locational precision. With GPS, the precise spot of an auto theft in the parking lot could be pinpointed, providing potentially useful information for protecting areas of the parking lot that are prone to theft. Crime inside the mall building could be reported with greater precision, whether in stores or in public spaces, provided a reasonably close line-of-sight GPS reading could be obtained. This type of "precision mapping" is already being performed in Charlotte, North Carolina, where GPS is used to plot exactly where crimes occur, even for locations without street addresses.

An application of GPS that is in development is in the area of probation and parole—tracking probationers and parolees if the terms of their release require limitations on their mobility. Indeed, future crime mapping applications will go beyond crime mapping per se and into other components of the criminal justice system, including corrections. One can expect to see the manipulation of spatial information and the application of new tools and technologies evolving in the coming decade. While developments in other branches of criminal justice will likely parallel spatial analysis developments in policing, we also can expect to see the development of specialized methods adapted to particular needs.

Postscript: The future of GIS in policing

When asked, "Why bother to discuss the future of GIS?," Clarke (1997) responded with three reasons that might apply equally to crime mapping:

  • The need to plan equipment purchases in the most efficient way, anticipating trends.

  • The need to stay abreast of the new field spawned by GIS called geographic information science.

  • The need to be prepared for cross- fertilization of different criminal justice fields using GIS.

Clarke suggested that we can classify speculation into two types:

  • The forward extension of current trends.

  • Pure speculation, with the likelihood that some ideas will become reality while others will fade away.

Clarke also noted that data will become more complete, more detailed, more timely, and more varied than ever before. This will be helpful to GIS as an "end user" of data—if the core data get richer, then possibilities for enhanced analysis also increase. But Clarke was referring to GIS in general. Can we have the same expectations for crime mapping?

Given that most crime data are already point defined (address-type), could they be improved in terms of spatial definition? Yes, at least marginally, through the use of GPS technology to remove address ambiguities, of which there are many. Whether locational data can be improved across the board may depend on the GPS protocols that develop, one police department at a time. Data quality will probably improve, and addresses will probably become more precise as more agencies use automated field reporting and integrated computer-assisted dispatching and records management systems.

More on GPS and policing

Equipping patrol units with GPS would mean that their locations could be known as often as each unit is "polled," or automatically asked to respond, perhaps every few minutes. This would be an excellent security device for officers, since their location could be determined at any time, and, if an officer were down or needed help, knowing his or her location would save valuable time.

But will GPS units typically be located in patrol cars? If so, some ambiguities in incident location will remain, since the car will not always be parked precisely where the incident takes place. If GPS units are hand held, or incorporated into officers' uniforms, accuracy may improve significantly. The caveat on GPS data, however, is that the physical environment may not permit a satellite reading owing to the presence of tall buildings or other obstacles. Such difficulties aside, the era of real-time access to spatially enabled crime data is rapidly approaching—a development that will force us to reconsider what we are doing and why and how we are doing it. This development is not without risks, such as the temptation to jump to premature conclusions on the basis of real-time, but possibly unconfirmed, information.

The Web: Already a force in the dissemination of police information

A development that may have the greatest impact on the manipulation of crime data may be the use of the Web for access to data that have already been geocoded and are in the public domain, such as census data, including census geography. A corollary development will likely be demands for local data on Web sites. Currently, police departments are split on this issue, with some routinely putting their less sensitive data on the Web, and others refraining from doing so. The power of the Web to facilitate data sharing will invite more open data dissemination protocols, but these will be offset to some extent by security and privacy concerns.

Public information revisited: How much public access to allow

A pervasive force at work in the background is the historical culture of policing that has generally frowned on easy public access to crime data. This reluctance is borne of several factors, including fear of misuse and misinterpretation; the indisputable need for confidentiality for some crimes, such as rape and juvenile offenses; fear of political reprisals when crime rates are increasing; and a reluctance to expend scarce resources on data dissemination. In the background was, and is, a certain degree of proprietorship regarding data and a somewhat natural reluctance to simply give information away, even though it might be in the public domain already, at least in theory. A subtext to this is the view that crime data should not be made available to the public if they do not have to be, since public disclosure only constitutes another potential source of problems.

On the other hand, undermining nondisclosure is the fact that many city and neighborhood newspapers routinely publish lists of local crimes, complete with addresses. The only missing link is the codification necessary to produce a citywide map. Criminal matters most often come before the courts and, in so doing, jump squarely into the public domain. In the long term, it is increasingly difficult to see how most crime data could be kept private, particularly data related to incidents for which there is no active investigative interest and no need to protect victims. Indeed, some departments that were secretive a decade ago are now beginning to put their data out on CD-ROMs or at least are talking about doing so. Others refuse to release data, even for legitimate apolitical research.

One certainty is that, in addition to technological and methodological innovations in crime mapping and in collateral fields that can be productively integrated into mapping methods, a debate about the disclosure and exposure of crime data will continue into the foreseeable future.

Multimedia and integration

Multimedia and integration are likely to be among the most prominent themes that evolve in the crime mapping arena over the next decade. Crime mappers will certainly take advantage of all the new technological advances, often using multimedia in ways that their developers might not have anticipated. Integration of various technologies, with data archiving (or warehousing) and data mining becoming more prominent, will be inevitable. Crime mapping may find itself merging into an enterprisewide GIS, as governments network access to data and standardize GIS platforms across entire jurisdictions to ensure compatibility and reduce costs. Change is certain. The only uncertainty is how the rate of change will vary from place to place.

Chapter 6: Crime Mapping Futures
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Mapping Crime: Principle and Practice, by Keith Harries, Ph.D., December 1999