Description: This coverage is derived from the flow accumulation grid. A threshold of 5,000 cells is applied to the flow accumulation grid, and a mask is created. Cells having a value greater than 5,000 are set to 1, and the remaining cells are set to "NODATA". The mask grid is then converted to the vector streamlines coverage. (also referred to as "synthetic streamlines"). Each synthetic streamline is also assigned a Pfafstetter number that identifies the basin subdivision level, relates associated seed points and catchments, and allows for analysis of upstream and downstream flow relationships with any other catchment or stream.