National Ocean Service
National Geodetic Survey
The United States has approximately 95,000 miles of coastline. One of the missions of NOAA's National Geodetic Survey (NGS) is to survey these coastal regions and to provide the Nation with accurate, consistent, up-to-date national shoreline.
The national shoreline provides the critical baseline data for demarcating America's marine territorial limits, including its Exclusive Economic Zone, and for the geographic reference needed to manage coastal resources and many other uses. These shoreline data are considered authoritative when determining the official shoreline for the United States. Until recently, acceptance of NOAA's shoreline data as a legal authority has been based upon NOAA's recognized expertise and court cases, but the public law passed by the U.S. Congress in 1998 provides NOAA with explicit authority to promulgate national standards for all information acquired for nautical charting purposes. The shoreline depicted on NOAA's nautical charts approximates the line where the average high tide, known as Mean High Water (MHW), intersects the coast. NGS' shoreline mapping also provides the line where Mean Lower Low Water (MLLW) intersects the coast.
At present, several different shoreline definitions are in use by various Federal, state, and local authorities. The use of inconsistent shoreline definitions between maps, charts, Geographic Information Systems (GIS), and other products can lead to confusion by users and can contribute to ill-informed decision making. Broader adoption of the NOAA-provided national shoreline is encouraged to help alleviate this problem.
The method used today by NGS to delineate the shoreline is stereo photogrammetry using tide-coordinated aerial photography controlled by kinematic Global Positioning System (GPS) techniques. This process produces a seamless, digital database of the national shoreline and a database of aerial photography.
NGS is exploring the use of new technologies and new methodologies to map the shoreline including:
For additional information on shoreline, also visit the NOAA Coastal Shoreline Website.
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