A designated line separating areas where development is encouraged and areas intended to remain undeveloped. This tool is used in urban planning to manage sprawl, preserve open space, and concentrate development within a defined area. For example, Portland, Oregon, has utilized this strategy to limit outward expansion and promote higher-density housing within its metropolitan area.
These boundaries provide several potential advantages. They can protect agricultural land, natural habitats, and scenic landscapes from being consumed by suburban expansion. Furthermore, they can encourage more efficient use of existing infrastructure, reduce transportation costs, and foster a sense of community by concentrating development. Historically, the implementation of these boundaries has been driven by concerns about environmental sustainability and the desire to maintain a distinct separation between urban and rural areas.