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Bathymetry for St. Catherines/Sapelo Sounds was derived from eighteensurveys containing 70,555 soundings. No surveys were omitted. The averageseparation between soundings was 52 meters. Fifteen of the eighteen surveysused dated from 1934. The remaining three surveys located in the east andsouth dated from 1974 and 1977. The total range of sounding data was 1.5meters to -20.1 meters at mean low water. Mean high water values between2.0 and 2.4 meters were assigned to the shoreline. Six points were found thatwere not consistent with the surrounding data. These were removed prior totinning. DEM grid values outside the shoreline (on land) were assigned nullvalues (-32676).St. Catherines/Sapelo Sounds have eleven 7.5 minute DEMs and a singleone degree DEM. The 1 degree DEMs were generated from the higherresolution 7.5 minute DEMs which covered the estuary. A DigitalElevation Model (DEM) contains a series of elevations ordered fromsouth to north with the order of the columns from west to east. TheDEM is formatted as one ASCII header record (A- record), followed bya series of profile records (B- records) each of which include ashort B-record header followed by a series of ASCII integerelevations (typically in units of 1 centimeter) per each profile.The last physical record of the DEM is an accuracy record(C-record).The 7.5-minute DEM (30- by 30-m data spacing) is cast on theUniversal Transverse Mercator (UTM) projection. It provides coveragein 7.5- by 7.5-minute blocks. Each product provides the samecoverage as a standard USGS 7.5-minute quadrangle but the DEMcontains over edge data. Coverage is available for many estuaries ofthe contiguous United States but is not complete.