Composite Shoreline

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Coverage

Continental U.S. and Hawaii.

Source Data

T-sheets, which are special-use planimetric or topographic maps that precisely define the shoreline and alongshore natural and man-made features, such as rocks, bulkheads, jetties, piers, and ramps. Where T-sheets are unavailable, NOAA’s extracted vector shoreline (EVS) was used to compile seamless shoreline coverage.

Tidal Datum

Mean high water (MHW)

Scale

1:5,000 to 1:20,000

Spatial Reference

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

Accuracy

The average accuracy of the measured benchmarks is 3.06 meters (10 feet), and this meets the National Ocean Service (NOS) guidelines for fixed aids to navigation and objects charted as landmarks. This accuracy is stricter than national standards and four times the accuracy of current U.S. Geological Survey 1:24,000-scale topographic maps. Because of this, the original T-sheets can be assumed to also meet NOS guidelines and to be very accurate in their depiction of the shoreline that existed at the time of the surveys.

Process Description

The 13,782 shoreline manuscripts (T-sheets) were scanned and converted to raster format. Raster manuscript scans were saved as .tif or .jpg at 250 or 1200 dpi respectively. ERDAS IMAGINE software was used for georeferencing. T-sheets were georeferenced in a geographic coordinate system, spheroid Clarke 1866, and North American Datum 1927. Georeferencing was not acceptable, with a total root mean square (RMS) error over 2.00. To confirm proper alignment, ERDAS IMAGINE 8.7 and Terraserver Imagery were used to check for alignment and validity of georeferencing work. ESRI ArcMap 9.1 was used to vectorize relevant shoreline features present in the shoreline raster files. During the vectorization process, attention to line work accuracy and attribute coding was assured through quality checks by a geographic information system analyst. The final vectors were re-analyzed in ESRI ArcMap 9.2 for quality control. Once all T-sheets for a state have been vectorized and georeferenced, the individual files are joined together so that all lines are connected through a process known as edge matching. Where gaps exist in the shoreline coverage, EVS data are used to complete the coverage. If multiple T-sheet files exist for a given area, priority is give to the most recent shoreline segment. T-sheets dating to pre-1950 are replaced with extracted vector shoreline data. All files are appended together into a statewide file.

Historical Composite Shoreline

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