The lack of attention paid to the physical, social, and economic conditions of the locations where gangs hang out is unfortunate for several reasons: (1) hanging out is a primary activity of all gangs; (2) the importance of physical space has never been truly quantified; and (3) gangs do not occupy the entirety of their neighborhood, but in small well defined localized areas within the community. The area in which the gang hangs out is described as being isolated from the rest of the neighborhood, suggesting that a lack of social control is important in determining the location of gang activity. This research maps the set space of urban street gangs in Pittsburgh, Pennsylvania. Most of the gangs in Pittsburgh call themselves either Bloods or Crips. The most important identifier is not so much the named gang one belongs to, but rather their affiliation with a smaller local “set.” Sets most often take their name from the street on which they hang out. The act of trespassing through a rival’s set space is a clear provocation for a violent confrontation. Any gang that had either victims or suspects involved in a gang-motivated homicide was included in this study. The first step in locating set space involved using a Geographic Information System (GIS) to construct street maps of the different neighborhoods where gangs were known to hang out. Informants were given a detailed street map and colored markers so that the individual could draw the boundaries of his set space. Results showed that gangs hung out in only small areas of entire neighborhoods. This has implications for community development and criminal justice responses to gangs. Gang injunctions are currently being used in Los Angeles to restrict certain individuals from congregating in particular areas. Careful analysis of the types of places where gangs hang out may provide insight into the formation and maturation process of urban street gangs. 5 figures, 15 references