This is a raster layer that defines the amount of upstream area (in number of cells) draining into each cell. The projection used is WGS84. The resolution of the dataset is 15 arc second (approximately 500 m at the equator).
Lehner, B., Verdin, K., Jarvis, A. 2006. HydroSHEDS Technical Documentation. World Wildlife Fund US, Washington DC. Available at http://hydrosheds.cr.usgs.gov