Development of effective strategies of crime control and prevention requires both a well-organized database and an efficient analytical tool for data manipulation and spatial analysis. Another critical concern is that, because crime prevention and control are most effectively carried out by localized agencies, the implementation of such an analytical tool must be cost-effective, i.e., the system must not only be affordable for each local police station, but it also can be maintained within the agency without the need of external assistance. Besides, in order for any system of crime analysis to be of practical use, its operations must be straightforward and user-friendly. With these concerns, the PC-based ArcView provides an ideal solution for the development of a crime analysis system. This paper presents the development of an ArcView interface designed specifically for crime analysis.
In general, the package of crime analysis should be designed to meet two main purposes. The first is the automation of routine procedures. Certain routine tasks, although relatively straightforward in operation, have to be undertaken by law enforcement agencies repeatedly on a regular basis. The automation of such tasks is important in that it will not only reduce the amount of operational time for designated officers, but also improve the accuracy of the crime-related database over time. For instance, the current typical procedure for crime reporting requires an officer to manually fill out a report form, take the form to the officer in charge of crime analysis for data entry. The officer may have to identify the address of the incident on a street map. Then, in order to illustrate the distribution of crime incidents for analysis, the officer may have to manually attach a pin onto a large wall map based on the location identified from the street map. This procedure can be much more efficiently handled by the crime analysis system. In this case, the report form can be entered into computer directly by the field officer, thus saving the time for filling out forms and entering into computer separately. The officer does not need to look into the street map for the location. It is automatically geocoded in ArcView. Furthermore, pin maps can be easily generated.
The second purpose of the system is to provide analytical capabilities that are essential to crime analysis. Common procedures of database manipulation, such as queries and selection of specific records, are available through built-in functions. Additional procedures implemented in the system allow the user to conduct a variety of spatial analyses based on the crime database.
TIGER-based street files come with numerous errors, including missing street segments, inaccurate or insufficient address ranges, typographic errors on the street names, etc. If the jurisdiction is not too large, such as the cases involving cities of median size, then correcting the street map is not a difficult job to do. The best thing about using a GIS to conduct crime analysis is that, once the street map is built and corrected, it can serve multiple purposes. For instance, the corrected street map can be used by other departments such as planning and public works. The correction of street map needs to be done only once, and then the map only requires periodical updating of new streets or new addresses.
In addition to the street map, several inter-related files must be integrated into the crime database. In general, the information to be incorporated includes crime incidents, suspects, victims, witnesses, and gang members. The database can be constructed in three different ways. First, an entry form is available for each data type, namely crime incidents, suspects, and gang members. The field officer equipped with a computer may enter the form directly into the system. In case the field officer does not carry a computer, he or she can fill out a blank form in the field and bring the form back to the office for report entry. Second, a previously constructed database can be imported into the system as long as the data format is compatible. The function is also useful when the agency already has another means of database construction and data entry. In the case, the crime analysis system is still useful for such an agency. A data conversion utility can be developed to convert whatever the agency's existing data format into a compatible format. Third, each field officer may create a file containing all his/her reporting cases. The files submitted by all the field officers can then be appended into the centralized system for analysis.
The diagram below shows the first part of the crime report entry form. The complete report form has the following sections: basic information of the incident, information about victims, witnesses, and suspects, detailed information about the incident, and information about the reporting officer. A scroll bar on the right allows the officer reporting the incident to move up or down on the form and type in the available information.
Both the Suspect Report and Gang Report modules provide an additional function for generation of wanted posters. Pictures of a suspect, the get-away car, the weapon, etc. can be scanned and entered into the database and saved as image files. The wanted poster may display some useful information about the suspect, along with pictures and the street map to help locating the suspect.
The diagram below shows a typical example where school locations are entered in a specific database. Schools are denoted by darker symbols while crime incidents are shown in red. Buffer zones can be generated from schools and, for instance, all drug-related crimes that are within 1,000 ft from schools can be highlighted.
Charts provide an efficient tool for viewing and examining crime statistics. For convenience, each analysis module includes a function which enables charts to be generated directly from the selected entries. Based on user-specified selection criteria, crime incidents, suspects, or gang members can be identified and mapped. Generation of charts according to the selected entries can be easily activated through a built-in procedure.
Cross referencing is another important function of the analysis modules. The three sets of data files (crimes, suspects, and gang members) can be cross-referenced simply by clicking a button. For instance, as a suspect or a known gang member is selected, the cross-referencing function allows the analyst to identify all the crime incidents in which the individual has been involved. Likewise, by selecting crimes that occurred in a target area, one may use the cross-reference function to identify all the suspects that are involved in the selected incidents. In this case, the purpose is to get a quick list of possible suspects that have committed similar crimes within the target geographic area, given the fact that a habitual offender tends to commit crimes in certain areas that the individual is relatively familiar with.
The diagram below shows a typical application of the cross-referencing function. In this example, a suspect is identified for a case under investigation. Once the suspect is identified from the suspect database, the cross-referencing allows all the crime incidents that involve the identified suspect to be identified. As the locations of related incidents are shown, the map becomes quite helpful for the crime analyst to determine the activity area of any suspect or gang members.
Another important function of the analysis modules is the display of images for cross examination. Scanned pictures and maps generated from the database can be visually analyzed through the image display tool. A combination of maps, pictures, and statistics provides the analyst with the capability of detecting spatial patterns and is useful for developing strategic plans of crime prevention and control.