NWI Wetlands

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.本数据集涵盖美国及其领土范围内湿地与深水栖息地的分布范围、大致位置及类型。这些数据按照考尔丁等人（Cowardin et al., 1979）提出的定义，勾勒出湿地与地表水的面积范围。国家湿地清查第二版（National Wetlands Inventory - Version 2）地表水与湿地清查数据集，是通过保留构成NWI（国家湿地清查）数字湿地空间数据图层的湿地与深水多边形，并将原本从原始NWI纸质地图中遗漏的线性湿地或地表水要素转换为窄多边形后重新纳入其中而生成的。此外，数据集还补充了经缓冲区处理转为多边形要素的水文数据，作为NWI未测绘的单线溪流要素的补充数据源，并完善分段连接。2012年后在华盛顿州（WA）、俄勒冈州（OR）、加利福尼亚州（CA）、内华达州（NV）及爱达荷州（ID）开展的湿地测绘工作，以及2015年后多数其他项目的测绘工作，均完整纳入了所有地表水要素，并非衍生数据。用于生成第二版数据集的线性水文数据集为美国地质调查局（U.S. Geological Survey）的国家水文数据集（National Hydrography Dataset, NHD）。关于第二版数据集所使用的NHD版本，以及第二版数据集的测绘范围，可在Wetlands_Project_Metadata要素类的"comments"（注释）字段中查询具体信息。由于将航空影像作为湿地探测主要数据源存在局限性，部分湿地栖息地未纳入国家测绘项目。这些栖息地包括分布在河口潮间带、潮下带及近岸海域的海草或沉水水生植被；部分深水礁群落（珊瑚或管栖蠕虫礁）也未纳入本次清查——由于其所处水深较大，航空影像无法探测到这类栖息地。按照政策，本机构还会排除《食品安全法》（Food Security Act）定义的部分"农用湿地"，或不符合考尔丁等人定义的湿地。如需了解湿地地图中纳入的农用湿地类型详情，请联系本机构的区域湿地协调员。本数据集需与Wetlands_Project_Metadata图层配合使用，该图层包含针对特定项目的湿地测绘流程，以及特定项目范围内用于湿地测绘的影像日期、比例尺与乳剂类型等相关信息。