National Wetlands Inventory
Ecological Services

Map Creation

Tips and Technical Information

  • Wetland features will display at 1:144,000 scale or larger.
  • As a function of the mapping display software, not all wetlands will be labeled.
  • Linear wetlands are not displayed on the Wetlands Mapper. Linear wetlands are wetland features that were originally captured as line segments rather than polygons. In certain situations, it was necessary to capture a wetland as a linear feature; when the size and shape of the wetland and the source scale were such that defining the wetland as a polygon was not possible. These linear data were originally kept as a separate feature class, but have now been incorporated into our new Surface Water and Wetlands Inventory dataset.  For more information please visit:

About the Wetlands Maps

The Service's topical wetland maps are graphic representations of the type, size and location of the wetlands and deepwater habitats in the United States. These maps have been prepared from the analysis of high altitude imagery in conjunction with collateral data sources and field work. The maps represent reconnaissance level information on the location, type, size of wetlands habitats such that they are accurate at the nominal scale of the 1:24,000 base map and the 1:63,360 base map for Alaska. A margin of error is inherent in the use of imagery; thus, detailed on-the-ground inspection of any particular site, may result in revision of the wetland boundaries or classification established through image analysis. The Service uses the Cowardin et al. (1979) definition of wetland. This definition is the standard for the agency and is the National Standard for wetland mapping, monitoring, and data reporting as determined by the Federal Geographic Data Committee in 1996.

For the purposes of adapting the wetland classification system to map form, a series of letter and number codes has been developed. These alpha-numeric codes correspond to the classification nomenclature that best describes the habitat. An example of how this mapping code is used is shown below:

wetland photo 
Lacustrine Aquatic Bed
NWI Map Classification Code: L  2  AB  G
Lacustrine (L) Littoral (2) Aquatic Bed (AB) Intermittently exposed (G)
Other Names/Identifiers: Lake Edge, Aquatic Bed

wetland photo 
Forested Wetland, Deciduous
NWI Map Classification Code: P  FO  1  C
Palustrine (P) Forested (FO) Broad leaved deciduous (1
Seasonally flooded (C)
Other Names/Identifiers: Hardwood Swamp

Last updated: July 26, 2016