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This image was generated from digital databases of land and sea-floor elevations on a 2-minute latitude/longitude grid (1 minute of latitude = 1 nautical mile, or 1.853 km). Assumed illumination is from the west; shading is computed as a function of the east-west slope of the surface with a nonlinear exaggeration favoring low-relief areas. A Mercator projection was used for the world image, which spans 390° of longitude from 270° West around the world eastward to 120° East; latitude coverage is ±80°. The resolution of the gridded data varies from true 2-minute for the Atlantic, Pacific, and Indian Ocean floors and all land masses to 5 minutes for the Arctic Ocean floor.

Major Sources of Data:

• The seafloor data between latitudes 72° North and 72° South are from the work of Smith and Sandwell (1977). These data were derived from satellite altimetry observations combined with carefully, quality-assured shipboard echo-sounding measurements, by Dr. Walter H.F. Smith, of the NOAA Laboratory for Satellite Altimetry and Dr. David T. Sandwell, of the Institute of Geophysics and Planetary Physics at the University of California, San Diego.
  For reference on the generation of these data, consult: W.H.F. Smith and D.T. Sandwell, "Global Sea Floor Topography from Satellite Altimetry and Ship Depth Soundings," Science Magazine, vol. 277, issue 5334, 1997.
• Seafloor data poleward of 72° are from the US Naval Oceanographic Office's (NAVOCEANO) Digital Bathymetric Data Base 5-minute (DBDB5).
• Land topography is from the GLOBE Project, an internationally designed, developed, and independently peer-reviewed global digital elevation model (DEM), at a latitude-longitude grid spacing of 30 arc-seconds (30"). The GLOBE Task Team was established by the Committee on Earth Observation Satellites (CEOS). It is part of Focus I of the International Geosphere-Biosphere Programme - Data and Information System. Primary contributors to the GLOBE database are: National Imagery and Mapping Agency (formerly Defense Mapping Agency), Fairfax, Virginia, USA Geographical Survey Institute, Tsukuba, Japan Australian Surveying and Land Information Group, Canberra, ACT, Australia Jet Propulsion Laboratory, Pasadena, California, USA University College London, UK DLR-German Remote Sensing Data Center, Oberpfaffenhofen, Germany NOAA National Geophysical Data Center (now the National Centers for Environmental Information), Boulder, Colorado, USA USGS EROS Data Center, Sioux Falls, South Dakota, USA