Description: This data set represents the extent, approximate location and type of wetlands and deepwater habitats in the United States and its Territories. These data delineate the areal extent of wetlands and surface waters as defined by Cowardin et al. (1979). The National Wetlands Inventory - Version 2, Surface Waters and Wetlands Inventory was derived by retaining the wetland and deepwater polygons that compose the NWI digital wetlands spatial data layer and reintroducing any linear wetland or surface water features that were orphaned from the original NWI hard copy maps by converting them to narrow polygonal features. Additionally, the data are supplemented with hydrography data, buffered to become polygonal features, as a secondary source for any single-line stream features not mapped by the NWI and to complete segmented connections. Wetland mapping conducted in WA, OR, CA, NV and ID after 2012 and most other projects mapped after 2015 were mapped to include all surface water features and are not derived data. The linear hydrography dataset used to derive Version 2 was the U.S. Geological Survey's National Hydrography Dataset (NHD). Specific information on the NHD version used to derive Version 2 and where Version 2 was mapped can be found in the 'comments' field of the Wetlands_Project_Metadata feature class. Certain wetland habitats are excluded from the National mapping program because of the limitations of aerial imagery as the primary data source used to detect wetlands. These habitats include seagrasses or submerged aquatic vegetation that are found in the intertidal and subtidal zones of estuaries and near shore coastal waters. Some deepwater reef communities (coral or tuberficid worm reefs) have also been excluded from the inventory. These habitats, because of their depth, go undetected by aerial imagery. By policy, the Service also excludes certain types of "farmed wetlands" as may be defined by the Food Security Act or that do not coincide with the Cowardin et al. definition. Contact the Service's Regional Wetland Coordinator for additional information on what types of farmed wetlands are included on wetland maps. This dataset should be used in conjunction with the Wetlands_Project_Metadata layer, which contains project specific wetlands mapping procedures and information on dates, scales and emulsion of imagery used to map the wetlands within specific project boundaries.
Description: This data set represents the extent and approximate location of historic wetland habitats in certain areas of the conterminous United States. The identification of these historic wetlands is limited by the methodology outlined in the associated Historic Wetlands Project Metadata and is not intended to be a comprehensive inventory of all historic wetlands. The U.S. Fish and Wildlife Service (Service) is the principal Federal agency that provides information to the public on the extent and status of the Nation's wetlands and provides stewardship for the wetlands data that comprise the Wetlands Layer of the National Spatial Data Infrastructure. In the formulation of this data layer, historic wetlands are defined as areas where there is evidence that a wetland once existed. This evidence can be from historical map information inventories of past wetland extent or other information collected that relate directly to data on wetland filling, drainage or other modifications. Historic wetlands have been identified using several different techniques depending on the availability and type of information used to locate these areas and user needs. For example, historical maps often provide information about past wetland extent or location and can be useful tools to identify historic wetlands. Historic wetlands have been identified as polygonal data. No linear features have been included. Historic wetland polygons are not classified as wetlands and have no wetland labels or attribution. Since these features no longer exist, boundary delineations are considered approximations based on topography, previously mapped information or indications of historic water levels.