The 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 EROS Data Center (EDC). 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 file is a replacement for the January 2003 map layer. This map layer was previously distributed as North America Shaded Relief. This layer is part of the 1997-2014 edition National Atlas of the United States.The Shaded Relief image was 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.