US Department of Commerce, NOAA; US Department of Commerce, NOAA. "National Geodetic Survey - Home". www.ngs.noaa.gov (بالإنجليزية الأمريكية). Archived from the original on 2021-01-30. Retrieved 2021-02-20.
US Department of Commerce, NOAA; US Department of Commerce, NOAA. "National Geodetic Survey - Home". www.ngs.noaa.gov (بالإنجليزية الأمريكية). Archived from the original on 2021-01-30. Retrieved 2021-02-20.