Schools and Crime

Schools and Crime

This chapter examines the usefulness of analyzing crime patterns by city blocks with chloropleth maps and statistical analyses. Three objectives are pursued. The first is to understand the social and environmental characteristics of crime locations. This effort links crime to communities. Such analyses help identify the limitations for affecting crime without basic alterations in areas' social structure and physical characteristics. To the extent that characteristics such as the ethnic composition and socioeconomic status of urban neighborhoods are “real” causes of crime, the impact of police activity alone will be limited. This objective also includes identifying the effects of other characteristics of high-crime places that may be changed by public agencies, such as zoning boards or social service agencies. An effort is made to estimate the effect of both fixed and malleable location characteristics on the incidence of crime.

The second objective is to illustrate crime's spatial variation within very small areas, specifically police sectors. Chloropleth maps will show the block-by-block variation in robberies. City blocks are “island blocks” for which the census reports data and are usually bounded by streets, roads, or other features. They correspond to the areas encompassed by a “walk around the block.” Even in police sectors that have few blocks, crime varies substantially. Chloropleth maps of crime by blocks have several advantages. The first advantage is that they permit viewing crime variations across small areas for an entire city or borough from a letter-size transparency. Attempting to detect patterns across large areas with pin maps is virtually impossible because incident symbols can cover the underlying map and conceal variations in crime. The second advantage is that there is no software-imposed limit on the number or hotness of hot spots. The block-chloropleth approach does not require a priori constraining hot spots to a certain minimum size. Finally, this approach [Page 154]respects a city's physical structure. Unlike circular buffers or hot spot ellipses, a hot spot for a block-chloropleth map is a city block and does not divide a house or yard.

Chloropleth mapping, however, has disadvantages. Hot spots can be omitted. Two street sides facing each other but in different blocks might each have a moderate amount of crime but not enough to make either block a hot spot. The two-side total of crimes, however, could be enough for a hot spot. Also, this approach can conceal the precise locations of crime. If all of a block's crime is on only one or two sides, this will not be portrayed in chloropleth maps. Once “hot blocks” are identified, overlaying crime incident points on an enlarged block map remedies this problem. These maps have their uses but should not be the sole cartographic method.

The third objective is to “go beyond a pretty map” whose interpretation can vary among individuals depending on their particular perspectives. The goal is to statistically evaluate the combined and separate associations of city block characteristics with crime. The power of statistical analysis is derived from its ability to assess the controlled associations and relative importance of particular areal characteristics with crime. Buffering or hot spot ellipses might identify places with high schools (Roncek & Faggiani, 1985; Roncek & Lobosco, 1983), bars (Roncek & Bell, 1981; Roncek & Maier, 1991; Roncek & Pravatiner, 1989), or subway stops (Block & Davis, 1996) as hot spots, but such analyses cannot indicate the importance of these places for crime throughout a city. Police and other public agencies may need to justify imposing new restrictions on bars, housing types, or other facilities. One method of demonstrating the need for change is by showing that crime is associated with a facility after taking other factors into account. This is the function of statistical analyses.

...