National Wetlands Inventory
Data Specifications
- Area of Coverage: The wetlands layer is a seamless digital data layer that contains information for approximately 82 percent of the conterminous U.S., 31 percent of Alaska, 100 percent of the windward islands of Hawaii, 62 percent of Puerto Rico and the U.S. Virgin Islands, and 100 percent of Guam and Saipan.
- Date(s) Available: Range from 1977 to present
- Format: Stored in ArcSDE geodatabase format and downloadable in ESRI Shapefile format
- Scale: 1:24,000
- Minimum Mapping Unit: In general, the minimum mapping unit is from one to three acres, depending on the wetland type and the scale and emulsion of the source aerial photography.
- Accuracy: The accuracy of image interpretation depends upon the quality of the imagery, the experience of the image analysts, the amount and quality of the collateral data, and the amount of ground-truth verification work conducted. Users should consult relevant metadata to determine the date of the source imagery used and any mapping problems.
Overview
Sample of NWI data mapped in Google Earth
The National Wetlands Inventory (NWI) is a series of topical maps that show wetlands and deepwater habitats. The goal of the NWI is to provide current geospatially referenced information on the status, extent, characteristics, and functions of wetland, riparian, deepwater, and related aquatic habitats in priority areas, in order to promote the understanding and conservation of these resources.
The maps have been used extensively to make resource management decisions at the federal, state, and local government levels, and they form the basis of the Wetlands Geospatial Data Layer of the National Spatial Data Infrastructure (NSDI).