Heritage Documentation Programs (HDP), part of the National Park Service, administers HABS (Historic American Buildings Survey), the Federal Government's oldest preservation program, and companion programs HAER (Historic American Engineering Record), HALS (Historic American Landscapes Survey), and CRGIS (Cultural Resources Geographic Information Systems). Documentation produced through the programs constitutes the nation's largest archive of historic architectural, engineering and landscape documentation. Records on nearly 40,000 historic sites, consisting of large-format, black and white photographs, measured drawings, and written historical reports, are maintained in a special collection at the Library of Congress. HDP conducts a nationwide documentation program in partnership with state and local governments, private industry, professional societies, universities, preservation groups, and other Federal agencies. The program assigns highest priority to sites of national significance that are in danger of demolition or loss by neglect, and to National Park Service properties. Documentation provides a permanent record of the nation's most important historic sites and large-scale objects. The Collection is unique in the strong support it enjoys from its institutional sponsors and the public, and is distinguished in its national scope, consistent format, archival stability, and continued growth. The documentation also contributes to wider recognition and appreciation of historic resources as National Historic Landmarks; provides baseline documentation for rehabilitation and restoration; and makes available well-researched materials for interpretation and illustration.