Zoning ordinances began as a way for cities to control the negative externalities associated with urban land uses, as well as a means of protecting property values. By separating residential districts from factories and retail areas, early city planners hoped to stabilize neighborhoods and preserve the value of the homes in a given residential area. As a suburban ideal of the private family home emerged, however, local governments began to use zoning laws to regulate the characteristics and lifestyles of people living in certain neighborhoods. By zoning districts for single-family use and defining “family” narrowly, localities began to zone for direct social control, allowing communities to exclude groups of people deemed “undesirable” as neighbors. Because single-family home ordinances with narrow definitions of family tend to zone out low-income individuals who cannot afford to live without roommates or extended family, and because historically, America’s poor have been disproportionately ethnic minorities, these ordinances tend to perpetuate class and racial segregation.