National Wetlands Inventory for the Conterminous United States

National Wetlands Inventory data delineates the extent, approximate location, and type of wetlands and deepwater habitats across the conterminous United States. The dataset was created by the State of Maryland based on definitions from Cowardin et al. (1979). The underlying data collection policy was last updated in 1992.

Use Cases

• Map wetland extent and type across the conterminous U.S. for conservation planning using geospatial habitat polygons.
• Analyze the proximity of development projects to protected deepwater habitats using location and type attributes.
• Train land cover classification models by using wetland type and location as labeled training data.
• Assess changes in wetland area over time by comparing this inventory's geospatial boundaries with newer surveys.

Strengths

• Covers the entire conterminous United States.
• Based on the established Cowardin et al. (1979) classification system.

Limitations

• Excludes certain habitats like seagrasses, submerged aquatic vegetation, and some deepwater reefs due to limitations of the primary aerial imagery source.
• By policy, excludes certain types of 'farmed wetlands', creating potential gaps in agricultural regions.
• The underlying data collection methodology and policy were last updated in 1992, making the inventory temporally stale.

Provenance

Source

State of Maryland, based on the U.S. Fish and Wildlife Service National Wetlands Inventory.

Collection Method

Primarily derived from the interpretation of aerial imagery, following the Cowardin et al. (1979) definition.

Freshness

Metadata record last updated on 2026-04-05, but the data collection policy is from 1992.

Geography

Conterminous United States.