Features describe information found on USGS topographic maps. These linkages enable the analysis and display of these water-related data in upstream and downstream order. It is part of a series of NHD user documentation. Features Features represent bodies of water, paths through which water flows, and related hydrographic entities.
Underpasses occur where features cross at different elevations.
NHD.NAT contains all underpasses. The lines representing network features, through which water flows in a known direction, are oriented in the direction of flow. The lines representing coastlines are usually oriented so that the sea or ocean is to the right. Reaches and reach codes provide the starting point. Reaches Reaches are segments of surface water with similar hydrologic characteristics.