The United States has an average elevation of roughly 2,500 feet (763m) above sea level, however there is a stark contrast in elevations across the country. Highest states Colorado is the highest state in the United States, with an average elevation of 6,800 feet (2,074m) above sea level. The 10 states with the highest average elevation are all in the western region of the country, as this is, by far, the most mountainous region in the country. The largest mountain ranges in the contiguous western states are the Rocky Mountains, Sierra Nevada, and Cascade Range, while the Appalachian Mountains is the longest range in the east - however, the highest point in the U.S. is Denali (Mount McKinley), found in Alaska. Lowest states At just 60 feet above sea level, Delaware is the state with the lowest elevation. Delaware is the second smallest state, behind Rhode Island, and is located on the east coast. Larger states with relatively low elevations are found in the southern region of the country - both Florida and Louisiana have an average elevation of just 100 feet (31m) above sea level, and large sections of these states are extremely vulnerable to flooding and rising sea levels, as well as intermittent tropical storms.

The U.S. Geological Survey (USGS) St. Petersburg Coastal and Marine Science Center conducted research to quantify the combined effect of all constructive and destructive processes on modern coral reef ecosystems by projecting future regional-scale changes in seafloor elevation along the Florida Reef Tract, Florida (FL). USGS staff used historical bathymetric point data from the 1930's (National Oceanic and Atmospheric Administration (NOAA) Office of Coast Survey, see Yates and others, 2017) and light detection and ranging (lidar)-derived data acquired in 2002 (Brock and others, 2006, 2007) to calculate historical seafloor elevation changes in the Upper Florida Keys (UFK) (Yates and others, 2017). Using those changes in seafloor elevation, annual rates of erosion were calculated for 13 habitat types found in the UFK reef tract. The annual rate of mean erosion for each habitat type was applied to a digital elevation model (DEM) extending from Port St. Lucie to Marquesas Key, FL that was modified from the NOAA National Centers for Environmental Information (NCEI) U.S. Coastal Relief Model coastal DEM (NOAA, 2001) to project future seafloor elevation (from 2001) along the Florida Reef Tract. Grid resolution for the DEM is 3-arc seconds (approximately 90 meters (m)).

Bathymetry for Apalachicola Bay was derived from eleven surveys containing 92,624 soundings. No surveys were omitted. The average separation between soundings was 80 meters. One survey dated from 1934; the rest dated from 1935. The total range of sounding data was 0.3 to -15.5 meters at mean low water. Mean high water values between 0.4 and 0.8 meters were assigned to the shoreline. Four points were found that were not consistent with the surrounding points. These were removed prior to tinning. DEM grid values outside the shoreline (on land) were assigned null values (-32676). Apalachicola Bay has sixteen 7.5 minute DEMs and two one degree DEMs. The 1 degree DEMs were generated from the higher resolution 7.5 minute DEMs which covered the estuary. A Digital Elevation Model (DEM) contains a series of elevations ordered from south to north with the order of the columns from west to east. The DEM is formatted as one ASCII header record (A- record), followed by a series of profile records (B- records) each of which include a short B-record header followed by a series of ASCII integer elevations (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 the Universal Transverse Mercator (UTM) projection. It provides coverage in 7.5- by 7.5-minute blocks. Each product provides the same coverage as a standard USGS 7.5-minute quadrangle but the DEM contains over edge data. Coverage is available for many estuaries of the contiguous United States but is not complete.

Bathymetry for the St. Johns River was derived from thirty-two surveys containing 158,931 soundings. No surveys were omitted. The average separation between soundings was 66 meters. Twenty-nine of the thirty-three surveys dated from 1935 to 1939. The remaining surveys, located in the north, dated from 1958 or 1959. The total range of sounding data was 0.6 meters to - 24.7 meters at mean low water. Mean high water values between 0.0 and 1.4 meters were assigned to the shoreline. Seven points were found that were not consistent with the surrounding data. These were removed prior to tinning. DEM grid values outside the shoreline (on land) were assigned null values (-32676). The St. Johns River has twenty-nine 7.5 minute DEMs and two one degree DEMs. The 1 degree DEMs were generated from the higher resolution 7.5 minute DEMs which covered the estuary. A Digital Elevation Model (DEM) contains a series of elevations ordered from south to north with the order of the columns from west to east. The DEM is formatted as one ASCII header record (A- record), followed by a series of profile records (B- records) each of which include a short B-record header followed by a series of ASCII integer elevations (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 the Universal Transverse Mercator (UTM) projection. It provides coverage in 7.5- by 7.5-minute blocks. Each product provides the same coverage as a standard USGS 7.5-minute quadrangle but the DEM contains over edge data. Coverage is available for many estuaries of the contiguous United States but is not complete.