National Shoreline

Coverage

Continental U.S., Alaska, Hawaiian Islands, Puerto Rico, and U.S. Virgin Islands.

Source Data

Aerial imagery, lidar, and high resolution satellite imagery

Tidal Datum

Mean high water (MHW) and mean lower low water (MLLW)

Scale

1:2,500 to 1:24,000

Spatial Reference

Geographic coordinate system; horizontal datum – North American Datum of 1983 (NAD83).

Accuracy

The absolute value of the overall predicted horizontal accuracy has not been determined. However, the reports associated with the project maps describe the process of producing the map source and include the horizontal control layout and, if aerotriangulated, the fit-to-control statistics. One may refer to the March 6, 1991, edition of the Journal of Coastal Research for an article entitled "Historical Shoreline Change: Error Analysis and Mapping Accuracy" for an independent accuracy assessment of vectorized NOS digital shoreline conducted by the Federal Emergency Management Agency and the University of Maryland.

Process Description

These data are derived from shoreline maps that were produced by NOS, including its predecessor agencies, and were based on analysts’ interpretations of imagery or field surveys. The NGS attribution scheme, "Coastal Cartographic Object Attribute Source Table (C-COAST)," was developed to synthesize the attribution of various sources of shoreline data into one attribution catalog. C-COAST is not a recognized standard but was influenced by the International Hydrographic Organization's S-57 Object-Attribute standard so the data would be more accurately translated into S-57.2 During the vectorization process, all adjoining shoreline maps in the project are displayed on a computer screen, and the shoreline is traced and coded appropriately. Maps within a project generally adjoin and, therefore, there is significant agreement of line work across the borders of the shoreline maps. This results in fewer errors related to the edge-matching process. Polygon labels and attributes are assigned to features containing area so that users may shade the data to determine land, water, or man-made features. All lines were attributed with feature code values that were translated to conform to NGS's Coastal Cartographic Object Attribute Source Table attribution scheme.