The grayscale North America shaded relief data were derived from the GTOPO30 elevation data. GTOPO30 is a global digital elevation model (DEM) with a horizontal grid spacing of 30 arc seconds (approximately 1 kilometer). GTOPO30 was derived from several raster and vector sources of topographic information. It was developed between 1993 and 1996 through a collaborative effort led by staff at the U.S. Geological Survey's Center for EROS. The following organizations participated by contributing funding or source data: the National Aeronautics and Space Administration (NASA), the United Nations Environment Programme/Global Resource Information Database (UNEP/GRID), the U.S. Agency for International Development (USAID), the Instituto Nacional de Estadistica Geografica e Informatica (INEGI) of Mexico, the Geographical Survey Institute (GSI) of Japan, Manaaki Whenua Landcare Research of New Zealand, and the Scientific Committee on Antarctic Research (SCAR). This layer is part of the 1997-2014 edition of the National Atlas of the United States. The grayscale shaded relief image were developed to portray the terrain of North America. It is intended for visual purposes only. The original GTOPO30 data must be used for conducting analysis and determining elevation values. This layer is presented in the WGS84 coordinate system for web display purposes. Downloadable data are provided in native coordinate system or projection.
