HydroSHEDS (Hydrological data and maps based on SHuttle Elevation Derivatives at multiple Scales)flow accumulation maps define amount of upstream area (in number of cells) draining into each cell for Asia. Drainage direction layers are used to define which cells flow into the target cell. Cells with a high flow accumulation are areas of concentrated flow and may be used to identify stream channels. The number of accumulated cells is essentially a measure of upstream catchment area. Because cell size of data set depends on latitude, the cell accumulation value cannot directly be translated into drainage areas in square kilometers. This data is derived from elevation data of the Shuttle Radar Topography Mission (SRTM) at 30 arc-second resolution approx. 1km at the equator.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.