"Input data from satellite observations, for example the terrain data used to build the catchments and river network, HydroSHEDS, are derived from the Shuttle Radar Topography Mission (SRTM) at 3 arc-sec resolution. The resolution of HydroSHEDS significantly exceeds that of existing global watershed and river maps. HydroSHEDS vector and rastor data sets include: stream networks, watershed boundaries, drainage directions, and anchillary data layers such as flow accumulations, distances, and river topology information." (Clark, R. M., 2013)
Clark, R. M. and Hakim, S. 2013. Securing Water and Wastewater Systems. Springer Science and Business Media. Page 140.