No coding is done outside District boundaries. In some quads one or more counties were not mapped. Unmapped areas are coded EX for external. The non-wetlands matrix is coded as U, for upland. Uplands areas may include hydric soils or drained wetlands.
Many vegetation types undergo rapid change, such as floating vegetation or cleared areas.
Many are changed by land use factors. Wetlands maps represent a baseline inventory, and are not edited to reflect changes. They do not delineate hydric soils, by any definition. Developed wetlands areas are usually not included. Local determinations always require field inspection.