GIS as a tool for data integration and exploration|
Chapter 4: Mapping Crime and Geographic Information Systems
A GIS is an ideal tool for bringing together various databases that share common geography. This function will become more useful as the importance of data integration is increasingly recognized. Not only is there a need for more data integration, but there is also a need for recognition that most data used in policing about land use, street centerlines, liquor establishments, bus routes, schools, subway stops, and so forth are likely to come from sources outside the police department. Finding these types of data and adapting them for crime analysis often take considerable initiative and may also demand attention to data quality. This raises the issue of metadata. This term refers to data about data. Metadata provide information about the databases that you use. (See "Minimum for Federal Geographic Data Committee-Compliant Metadata.") Metadata standards are developed under the auspices of the Federal Geographic Data Committee (FGDC), a unit that coordinates development of the National Spatial Data Infrastructure (NSDI). (See the appendix for additional resources.)
All data with common geography can
be overlaid. These layers may be manipulated-moved up or down, added or removed (permanently or temporarily), or made to become visible or invisible only when the map is shown at a specified scale. As noted on page 92, "What Is a GIS?," a fundamental concept in GIS
is layering. The various forms of this process can provide a GIS with much of its power and flexibility.
Combining data in geographic space provides opportunities for data exploration and analysis that are lacking when geographic data are missing. An analyst may want to see how robbery locations relate to the locations of convenience stores. Although this information may be in different databases, it can be brought together in GIS and the locations subjected to the necessary analysis. For example, buffer zones could be constructed at a specified distance around each convenience store, and the number of robberies in each zone counted. Then the percentage of robberies proximal to stores could be calculated to provide an indication of the importance of this type of store as a robbery target. The possibilities offered by this type of spatial analysis are virtually unlimited. They include hot spot analysis, stolen auto recovery directions and
distances, delineations of gang turfs,
calculations of area-specific rates, the
construction of crime or other "surfaces," network analyses, boundary determinations, and others mentioned elsewhere.