One of the primary missions of the National Ocean Service (NOS) and its predecessor agencies has been to accurately survey the coast of the United States. Beginning in the late 1930's, metric aerial photographs have become the primary source material for coastal survey maps and digital cartographic feature files. Photographic surveys replaced plane table field surveys because they could be completed faster and less expensively. The metric-quality vertical aerial photographs are acquired by the National Geodetic Survey (NGS) and their contractors and are maintained by the NGS. These photographs are used for a variety of geo-positioning application including shoreline delineation, marine planning, mapping water depths, topographic mapping, mapping seabed characteristics, and locating features or obstructions to ensure the safety of marine and air navigation. NGS's area of photogrammetric responsibilities includes all coastal regions, including the Great Lakes and their connecting navigable waterways. This represents approximately 95,000 miles of shoreline. NGS maintains a library of all vertical aerial photographic surveys of the coast dating back to1945 1942. There are currently over 500,000 photographs in the library with additional photographs being acquired each year. All photographs are available to the public for purchase.