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Bathymetry for Mississippi Sound was derived from thirty-three surveyscontaining 371,210 soundings. Five overlapping, older, less accurate surveyswere omitted before tinning. The average distance between soundings was 89meters. The thirty-three surveys used dated from 1960 to 1979. The range ofsoundings for the surveys used was 0.8 meters to -17.6 meters at mean lowwater. A mean high water value of 0.5 meters was assigned to the shoreline.Twenty-five points were found that were not consistent with the surroundingpoints. These were removed prior to tinning. DEM grid values outside the shoreline (on land) were assigned null values (-32676).Mississippi Sound has forty-four 7.5 minute DEMs and three one degreeDEMs. The 1 degree DEMs were generated from the higher resolution 7.5minute DEMs which covered the estuary. A Digital Elevation Model(DEM) contains a series of elevations ordered from south to northwith the order of the columns from west to east. The DEM isformatted as one ASCII header record (A- record), followed by aseries of profile records (B- records) each of which include a shortB-record header followed by a series of ASCII integer elevations(typically in units of 1 centimeter) per each profile. The lastphysical 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.