"Drug Dealing in Open-Air Markets provides an overview of the problem and discusses the factors that increase the risks of drug dealing in open-air markets. The guide also provides questions for consideration when conducting an analysis of your open-air drug market problem and reviews responses to the problem and what is known about them from evaluative research and police practice."
Problem-Oriented Guides for Police, Problem-Specific Guides Series No. 31
Office of Community Oriented Policing Services: http://www.cops.usdoj.gov/