"Since 1996, the National Youth Gang Center (NYGC) has conducted an annual survey of law enforcement agencies to assess the extent of gang problems by measuring the presence, characteristics, and behaviors of local gangs in jurisdictions throughout the United States. The National Youth Gang Survey (NYGS) is based on a nationally representative sample of law enforcement agencies serving larger cities, suburban counties, smaller cities, and rural counties. This Web resource contains analysis and findings from the ongoing National Youth Gang Surveys. Numerous charts and descriptions are provided as a resource for understanding gang problems. Standard questions asked each year include the following in these charts: the presence or absence of gang activity, the number of gangs and gang members, the number of homicides involving gangs, and the assessment of the gang problem from the previous year. Other questions asked are also included in these charts; however, these questions are asked intermittently and not every survey year. The questions include year of gang onset, demographic characteristics of gang members, gang unit operation, gang-member migration patterns, gang-related offenses, definitional characteristics of a gang, and designations of gang membership."
U.S. Department of Justice National Gang Center: http://www.nationalgangcenter.gov/