Temple University Department of Criminal Justice Spatial Clustering of Illegal Drug Dealers: Swarming for Safety or Agglomeration for Profit Dr. George F. Rengert Department of Criminal Justice Temple University Philadelphia, PA. 19122 [email protected]
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Temple University Department of Criminal Justice Spatial Clustering of Illegal Drug Dealers: Swarming for Safety or Agglomeration for Profit Dr. George.
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Where can illegal drug markets locate? Folk wisdom: any where they want to. Scientific knowledge: any where they want to as
long as: Safe from neighbors and detection by police. Profits can be made.
Safest areas to sell drugs generally thought to be in socially disorganized areas. If not socially disorganized, may experience
resistance from neighbors. Example from North Philadelphia:
Temple UniversityDepartment of Criminal Justice
Temple UniversityDepartment of Criminal Justice
But most socially disorganized areas may be least profitable areas. Lack local demand—abandoned houses.
Drug dealing can lead to abandoned houses as more people sell than buy houses in this community.
Would you buy one of these houses located in a drug sales area of North Philadelphia?
Temple UniversityDepartment of Criminal Justice
Temple UniversityDepartment of Criminal Justice
Temple UniversityDepartment of Criminal Justice
The following is an example of housing abandonment measured by tax delinquency around a drug sales area.
Temple UniversityDepartment of Criminal Justice
Temple UniversityDepartment of Criminal Justice
Temple UniversityDepartment of Criminal Justice
Which is it, profit or social disorganization?
Critical issues concerning profits in retail operations: location, location, location. Good locations allow:
ready access attract large numbers of customers increase the potential sales of retail outlets.
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Retail market analysts commonly use demographic variables to predict market share = Demographic Profile. Who is likely to purchase illegal drugs?
Young adults aged 15 to 29. High school drop-outs. Unemployed.
Marketing geographers have developed several strategies for determining optimal locations of retail firms.
Location-allocation model most often used. Includes: the objective function, demand points,
feasible sites, a distance matrix, and an allocation rule.
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We use the objective function of maximizing sales volume by minimizing distance to potential customers identified by the Demographic Profile.
Data from Wilmington, Delaware. Demand points = centroids of census tracts. Distance matrix = distance between centroids of
. census tracts.
Allocation rule = customers assigned to the census tract that minimizes total distance traveled by potential customers for illegal drugs.
Assumption = all users in city purchase drugs at
this census tract
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Would have to travel the fewest person-miles if illegal drug market was located in census tract 1600.
This tract was fourth from the highest in reality.
Limitations of the simple form of location-allocation model: Planar model = any location in city is a potential
site. Residents of expensive housing areas not likely.
Masked out areas where medium housing values above average.
Local addicts will travel any distance for drugs. Assigned zero to distance if beyond a mile, 1 if less.
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Distance matrix is replaced with zeros and ones. Two clusters of census tracts identified:
2200, 2300, and 1400. 602 and 601. Surprise: not in the center of the city.
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The analysis yielded two clusters of census tracts. The census tracts that ranked first, second and
third formed the first cluster. The census tracts that ranked fifth and sixth the
second. The preceding map portrayed this analysis.
It is not census tract 600 or 1600 that are in the center of the city.
Rather it is a group of census tracts that are in the center of a population of potential drug users.
Rather large areas. We need specific sites for our drug market. Requires more refined analysis possible with GIS.
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What can Geographic Information Systems do for us? Compare traditional analysis with what possible
with GIS:
Traditional analysis assigns features to census space. Census tracts. Block groups. Block faces.
Census boundaries are set and determine the spatial nature of the analysis.
Temple UniversityDepartment of Criminal Justice
Temple UniversityDepartment of Criminal Justice
Refined method: Create GIS buffers about features and allocate
proportion of area of tract that is within buffer. Advantages:
Feature does not have to be in tract to impact it.
Impact is proportional to size of tract.
Disadvantages:
Assumes impact uniformly distributed across entire tract.
Proportion not site specific.
Temple UniversityDepartment of Criminal Justice
Temple UniversityDepartment of Criminal Justice
GIS method: Create new geographies with buffers around
features. Create ‘interaction effects’ with overlays of
buffers. Advantages:
Does not assume effect is uniform over census tract. Buffers can be sized to reflect spatial reach of a feature.
Disadvantages: New geographies vary markedly in size. Small slivers created that lack geographic meaning. Zero counts overrepresented.
Temple UniversityDepartment of Criminal Justice
Temple UniversityDepartment of Criminal Justice
Drug Market Analysis of Wilmington, Delaware, GIS. Initially start with census data at block group level.
Local Demand: 1. Percent of population age 14 to 29. 2. Unemployed males. 3. Percent of population over age 18 with less than a high school education. 4. Median Income. 5. Number of children under age 5 living in poverty. R2 = .467
Temple UniversityDepartment of Criminal Justice
Identify features that attract potential drug users.
Routine activities create ‘crime generators.’ Schools, taverns, homeless shelters, etc.
Create buffers around these features to determine their areal reach if any.
Use location quotients to determine if feature associated with spatial aggregation of drug dealers.
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LQ = CR / CN
CR = Number of drug arrests per square mile in
GIS identified area.
CN = Number of drug arrests per square mile in
entire city.
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Accessibility Buffers Location Quotients
400-ft Major Roads 1.49 600-ft Major Roads 1.30 800-ft Major Roads 1.20