The North American Atlas – Basin Watersheds data set shows watersheds in North America at 1:10,000,000.  A watershed is an area encompassing part or all of a surface drainage basin, a combination of drainage basins, or a distinct hydrologic feature.  Watersheds are mapped in a hierarchical system, with the largest units encompassing the entire drainage areas of major rivers or river systems, or encompassing seaboard areas.  Within these large units, subsequently smaller units encompass the drainage areas of smaller rivers and streams.  Watersheds are classified differently in Canada, Mexico and the United States; the data set includes a continental classification (the North American Watershed, or NAW level), as well as the classification unique to each country.  This data set was compiled from each country’s watershed file and adjustments were made to the data to resolve misalignments and mismatches across international borders.