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# How to Identify Hot Spots and Read a Crime Map

Date Published
May 24, 2010

Savvy community policing officers may know which places in their beat tend to be trouble spots. Many are keenly aware of signs of unusual activity in shops, stores, street corners, warehouses and other locations they regularly patrol. Law enforcement executives and crime analysts who do not patrol beats can also identify these hot spots to help the community formulate responses.

## Maps and Geographic Information Systems

Analysts can create a variety of maps that visualize different aspects of a particular location. Density maps, for example, show where crimes occur without dividing a map into regions or blocks; areas with high concentrations of crime stand out.

Analysts use geographic information systems (GIS) to combine street maps, data about crime and public disorder, and data about other features such as schools, liquor stores, warehouses and bus stops. The resulting multidimensional maps produce a visual display of the hot spots. The GIS places each crime within a grid system on a map and colors each cell based on how many incidents occurred in that area.

See Reading a Crime Map.

Although high-crime areas may often be defined as hot spots based on past experiences of officers or the characteristics of those areas, GIS allow law enforcement agencies to more accurately pinpoint hot spots to confirm trouble areas, identify the specific nature of the activity occurring within the hot spot and then develop strategies to respond.

## Statistical Tests

Analysts can use statistical software to determine whether an area with a high number of crimes is a hot spot or whether the clustering of those crimes is a random occurrence.

CrimeStat III and GeoDa are two computer software programs for hot spot analysis.

## Reading a Crime Map

Maps of hot spots areas convey powerful messages to their readers. These messages are conveyed by various symbols:

• Points (or dots) draw attention to specific places and suggest that places with many points have local problems unique to that location. A point conveys the message that the hot spot is located at this exact location and should be the focus of police efforts.
• A shaded street segment suggests that the chances of crime are roughly equal along the entire segment and police efforts should focus along this segment but not along other streets.
• A shaded area, which shows discrete distributions of crime for particular areas such as beats, precincts, districts, counties, or census blocks, also suggests equivalent risks of crime throughout the area with a dramatic reduction in risk at the border. It suggests that police activity throughout the area is appropriate.
• A density surface, which depicts crime estimates of frequency or risk as a surface of color gradients that imply a high level of crime activity in its center which gradually tapers off in the outer areas. It directs police attention to the center and its surroundings.

Each way of depicting hot spots is connected with useful theories on why crimes occur in hot spots, each of which suggests different types of police action. Recognition of these links in mapping practice can lead to better use of crime maps.

See chapter 1 of Mapping Crime: Principles and Practice for more on how to read and understand crime maps.

Date Published: May 24, 2010