They are each classified by a specific Feature Type, which has its own unique Feature Code. Features can be either points, lines, or areas. Groups of features then form reaches. Reaches are composed of hydrographic entities which have similar hydrologic characteristics. Each reach also has a unique identifying reach code.
Transport reaches represent the conveyance of water through the river network.
Coastline reaches are located along the major coastlines of the United States and they allow for the storage of information necessary to coastlines. Waterbody reaches consist of more than one waterbody region that allows for the relation of additional information to the waterbody. The reaches provide a basis for linking water related data to the drainage network. This is accomplished by using flow relationships, which relate individual transport and coastline reaches to each other. The NHD coverage contains nodes, lines, and polygons which create the network topology.