The WA National Hydrography Dataset (NHD) Flowline layer is developed at a resolution of 1:24,000–4,800 and contains linear watercourses representing streams, rivers, canals, ditches, coastline, pipelines, and artificial paths.

The WA National Hydrography Dataset (NHD) Flowline layer is developed at a resolution of 1:24,000–4,800 and contains linear watercourses representing streams, rivers, canals, ditches, coastline, pipelines, and artificial paths (centerlines through water polygon features such as lakes, estuaries, or double-banked streams). The Washington State NHD is the State standard (OCIO policy 161.03) hydrography layer. Strahler StreamOrder and FeatureType (FType) are commonly used for symbolization. (StreamOrder ranges from the smallest streams = 1, to the largest Columbia River = 10).