Historic districts in the United States are designated historic districts recognizing a group of buildings, properties, or sites by one of several entities on different levels as historically or architecturally significant. Buildings, structures, objects and sites within a historic district are normally divided into two categories, contributing and non-contributing. Districts vary greatly in size: some have hundreds of structures, while others have just a few. The U.S. federal government designates historic districts through the United States Department of Interior under the auspices of the National Park Service. Federally designated historic districts are listed on the National Register of Historic Places, but listing usually imposes no restrictions on what property owners may do with a designated property. State-level historic districts may follow similar criteria (no restrictions) or may require adherence to certain historic rehabilitation standards. Local historic district designation offers, by far, the most legal protection for historic properties because most land use decisions are made at the local level. Local districts are generally administered by the county or municipal government. History The first U.S. historic district was established in Charleston, South Carolina in 1931, predating the U.S. federal government designation by more than three decades. Charleston city government designated an "Old and Historic District" by local ordinance and created a board of architectural review to oversee it. New Orleans followed in 1937, establishing the Vieux Carré Commission and authorizing it to act to maintain the historic character of the city's French Quarter. Other localities picked up on the concept, with the city of Philadelphia enacting its historic preservation ordinance in 1955. The regulatory authority of local commissions and historic districts has been consistently upheld as a legitimate use of government police power, most notably in Penn Central Transportation Co. v. City of New York (1978). The Supreme Court case validated the protection of historic resources as "an entirely permissible governmental goal." In 1966 the federal government created the National Register of Historic Places, soon after a report from the U.S. Conference of Mayors had stated Americans suffered from "rootlessness." By the 1980s there were thousands of federally designated historic districts. Some states, such as Arizona, have passed referendums defending property rights that have stopped private property being designated historic without the property owner's consent or compensation for the historic overlay. Property types Historic districts are generally two types of properties, contributing and non-contributing. Broadly defined, a contributing property is any