An Error Assessment of Vector Data Derived front Scanned National Ocean Service Topographic Sheets

Richard C. Daniels, Robert H. Huxford


The National Oceanic and Atmospheric Administration, National Ocean Service (NOS) has undertaken a data-rescue project to convert historical topographic sheets (T-sheets) from paper or cloth to a digital format. The original maps have been scanned and saved as raster images. These images have been registered and the line work vectorized using heads-up digitizing methods to obtain X, Y coordinate pairs that delineate the location of the shorelines depicted on the original maps. A methodology is described here for obtaining error estimates for the derived vector data. The error assessment methodology uses the coordinates obtained for survey stations digitized from the scanned T-sheets and compares these coordinates to those published by the National Geodetic Survey. Differences between published coordinates for survey stations and those measured from the T-sheets have been calculated and descriptive statistics obtained. In southwest Washington and northwest Oregon the mean error for 1926/27 and 1950-era T-sheets is ±3 m for 1:10,000 scale sheets and ±6 m for 1:20,000 scale sheets.


National Ocean Service; US. Coast & Geodetic Survey; historical shoreline delineation; shoreline position; mean high water line; Oregon; Washington

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