This raster layer is a void-filled digital elevation model (DEM) of North America at 15 arc-seconds resolution. Elevation is expressed in meters and referenced to the WGS84 EGM96 geoid. The primary data s ource of HydroSHEDS is the digital elevation model of the Shuttle Radar Topography Mission. SRTM elevation data were obtained by a specially modified radar system that flew onboard the Space Shuttle Endeavor during an 11-day mission in February of 2000. Regions of no-data (voids), specifically mountainous regions, or those over large water bodies prevented the production of reliable elevation data. The existence of no-data in the DEM causes significant problems for deriving hydrological products, which require continuous flow surfaces. Therefore, a void-filling procedure has been applied to provide a continuous DEM for HydroSHEDS. The goal of developing HydroSHEDS was to generate key data layers to support regional and global watershed analyses, hydrological modeling, and freshwater conservation planning at a quality, resolution and extent that had previously been unachievable. HydroSHEDS has been developed by the Conservation Science Program of World Wildlife Fund (WWF), in partnership with the U.S. Geological Survey (USGS), the International Centre for Tropical Agriculture (CIAT), The Nature Conservancy (TNC), and the Center for Environmental Systems Research (CESR) of the University of Kassel, Germany. For more information please refer to the HydroSHEDS Technical Documentation: Lehner, B., Verdin, K., Jarvis, A. (2006): HydroSHEDS Technical Documentation. World Wildlife Fund US, Washington, DC. Available at http://hydrosheds.cr.usgs.gov. Please also visit http://www.worldwildlife.org/hydrosheds and http://hydrosheds.cr.usgs.gov for information on data download and status reports. This layer is presented in the WGS84 coordinate system for web display purposes. Downloadable data are provided in native coordinate system or projection.