NWI digital data files are records of wetlands location and classification as developed by the U.S. Fish & Wildlife Service. SoilMap displays the wetland polygons portion of the NWI dataset. A text option is available which displays a wetland classification label for each polygon.

Click here for complete source metadata.

NWI maps do not show all wetlands, but attempt to show most photointerpretable wetlands given considerations of map/photo scale and wetland delineation practices. A target mapping unit (tmu) is an estimate of the size class of the smallest group of wetlands that NWI attempts to map consistently; it is not the smallest wetland mapped. Recognize that some wetland types are conspicuous and readily mapped (e.g., marshes and ponds) and smaller ones may be mapped. Drier wetlands and forested wetlands (especially evergreen) are more difficult to photointerpret and larger ones may be missed. The tmu also varies with photo scale; in forested regions, the tmu may be 3-5 acres (1:80K photos), 1-3 acres (1:58K), or 1 acre (1:40K). NWI maps should show most wetlands larger than the tmu. In the treeless prairies, a 1/4 acre tmu is possible due to the openness of terrain and occurrence of wetlands in distinct depressions. Take notice of the photo scale/type used to make the maps (see legend) and realize that black and white photos tend to yield more conservative interpretations than color infrared film. Most farmed wetlands (e.g., mucklands) are usually not mapped, except for pothole-type wetlands, cranberry bogs, and diked former tidelands (Sacramento Valley). Partly drained wetlands are conservatively mapped due to photointerpretation limitations. No attempt was made to identify regulated wetlands from other wetlands. Recognize that maps produced through photointerpretation are not as accurate as one prepared from on-the-ground surveys, so NWI boundaries are generalized.

The NWI Wetlands layer is only visible at map scales larger than 1:80,000.

For More Information - Visit the National Wetlands Inventory page.
Wetland Classification Codes - Classification Code system page.

Note: All SoilMap source data has been projected to an Albers Conical Equal Area projection with the following parameters.

PROJCS["Albers Conical Equal Area",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Albers"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-78.0],PARAMETER["Standard_Parallel_1",40.0],PARAMETER["Standard_Parallel_2",42.0],PARAMETER["Latitude_Of_Origin",39.0],UNIT["Meter",1.0]]

The data and documentation on SoilMap are provided 'as is' and the User assumes the entire risk as to their quality and performance. SoilMap source data was produced at a variety of scales and may not be suitable for use at larger scales.