Are you working with US FWS NWI data? If so then this document explaining the various classification & map codes is a must have. A series of letter and number codes has been developed to adapt the national wetland classification system to map form. These alpha-numeric codes correspond to the classification nomenclature that best describes the habitat
WETLANDS AND DEEPWATER HABITATS CLASSIFICATION SYSTEM SUBSYSTEM CLASS SUBCLASS |- RB=Rock Bottom 1=Bedrock | 2=Rubble | |- UB=Unconsolidated Bottom 1=Cobble-Gravel | 2=Sand | 3=Mud | 4=Organic | |-- 1=SUBTIDAL----|- AB=Aquatic Bed 1=Algal | | 3=Rooted Vascular | | 5=Unknown | | Submergent | | | |- RF=Reef 1=Coral | | 3=Worm | | | |- OW=Open Water/Unknown Bottom (used on older | maps) M=MARINE--------| | | | |- AB=Aquatic Bed 1=Algal | | 3=Rooted Vascular | | 5=Unknown | | Submergent | | | |- RF=Reef 1=Coral |-- 2=INTERTIDAL--| 3=Worm | |- RS=Rocky Shore 1=Bedrock | 2=Rubble | |- US=Unconsolidated Shore 1=Cobble-Gravel 2=Sand 3=Mud 4=Organic SYSTEM SUBSYSTEM CLASS SUBCLASS |- RB=Rock Bottom 1=Bedrock | 2=Rubble | |- UB=Unconsolidated Bottom 1=Cobble-Gravel | 2=Sand | 3=Mud | 4=Organic | |-- 1=SUBTIDAL----|- AB=Aquatic Bed 1=Algal | | 3=Rooted Vascular | | 4=Floating | | Vascular | | 5=Unknown | | Submergent | | 6=Unknown Surface | | | |- RF=Reef 2=Mollusc | | 3=Worm | | | |- OW=Open Water/Unknown Bottom (used on older | maps) E=ESTUARINE-----| | | | |- AB=Aquatic Bed 1=Algal | | 3=Rooted Vascular | | 4=Floating | | Vascular | | 5=Unknown | | Submergent | | 6=Unknown Surface | | | |- RF=Reef 2=Mollusc | | 3=Worm | | | |- SB=Streambed 3=Cobble-Gravel | | 4=Sand | | 5=Mud | | 6=Organic | | | |- RS=Rocky Shore 1=Bedrock | | 2=Rubble | | |-- 2=INTERTIDAL--|- US=Unconsolidated Shore 1=Cobble-Gravel | 2=Sand | 3=Mud | 4=Organic | |- EM=Emergent 1=Persistent | 2=Nonpersistent | |- SS=Scrub-Shrub 1=Broad-Leaved | Deciduous | 2=Needle-Leaved | Deciduous | 3=Broad-Leaved | Evergreen | 4=Needle-Leaved | Evergreen | 5=Dead | 6=Indeterminate | Deciduous | 7=Indeterminate | Evergreen | |- FO=Forested 1=Broad-Leaved Deciduous 2=Needle-Leaved Deciduous 3=Broad-Leaved Evergreen 4=Needle-Leaved Evergreen 5=Dead 6=Indeterminate Deciduous 7=Indeterminate Evergreen SYSTEM SUBSYSTEM CLASS SUB
CLASS |- RB=Rock Bottom 1=Bedrock | 2=Rubble | |- UB=Unconsolidated Bottom 1=Cobble-Gravel | 2=Sand |--1=TIDAL--------| 3=Mud | | 4=Organic | | | |-*SB=Streambed 1=Bedrock | | 2=Rubble | | 3=Cobble-Gravel |--2=LOWER | 4=Sand | PERENNIAL----| 5=Mud | | 6=Organic | | 7=Vegetated | | | |- AB=Aquatic Bed 1=Algal R=RIVERINE------|--3=UPPER | 2=Aquatic Moss | PERENNIAL----| 3=Rooted Vascular | | 4=Floating | | Vascular | | 5=Unknown | | Submergent |--4=INTERMITTENT-| 6=Unknown Surface | | | |- RS=Rocky Shore 1=Bedrock | | 2=Rubble | | | |- US=Unconsolidated Shore 1=Cobble-Gravel |--5=UNKNOWN | 2=Sand | PERENNIAL----| 3=Mud (used on older | 4=Organic maps) | 5=Vegetated | |-**EM=Emergent 2=Nonpersistent | |- OW=Open Water/Unknown Bottom (used on older | maps) |-*STREAMBED is limited to TIDAL and | INTERMITTENT SUBSYSTEMS, and comprises | the only CLASS in the INTERMITTENT SUBSYSTEM. | |-**EMERGENT is limited to TIDAL and LOWER | PERENNIAL SUBSYSTEMS. SYSTEM SUBSYSTEM CLASS SUBCLASS |- RB=Rock Bottom 1=Bedrock | 2=Rubble | |- UB=Unconsolidated Bottom 1=Cobble-Gravel | 2=Sand | 3=Mud | 4=Organic | |-- 1=LIMNETIC----|- AB=Aquatic Bed 1=Algal | | 2=Aquatic Moss | | 3=Rooted Vascular | | 4=Floating | | Vascular | | 5=Unknown | | Submergent | | 6=Unknown Surface | | | |- OW=Open Water/Unknown Bottom (used on older | maps) L=LACUSTRINE----| | | | |- RB=Rock Bottom 1=Bedrock | | 2=Rubble | | | |- UB=Unconsolidated Bottom 1=Cobble-Gravel | | 2=Sand | | 3=Mud | | 4=Organic | | | |- AB=Aquatic Bed 1=Algal | | 2=Aquatic Moss | | 3=Rooted Vascular | | 4=Floating |-- 2=LITTORAL----| Vascular | 5=Unknown | Submergent | 6=Unknown Surface | |- RS=Rocky Shore 1=Bedrock | 2=Rubble | |- US=Unconsolidated Shore 1=Cobble-Gravel | 2=Sand | 3=Mud | 4=Organic | 5=Vegetated | |- EM=Emergent 2=Nonpersistent | |- OW=Open Water/Unknown Bottom (used on older maps) SYSTEM SUBSYSTEM CLASS SUBCLASS |- RB=Rock Bottom 1=Bedrock | 2=Rubble | |- UB=Unconsolidated Bottom 1=Cobble-Gravel | 2=Sand | 3=Mud | 4=Organic | |- AB=Aquatic Bed 1=Algal | 2=Aquatic Moss | 3=Rooted Vascular | 4=Floating | Vascular | 5=Unknown | Submergent | 6=Unknown Surface | |- US=Unconsolidated Shore 1=Cobble-Gravel | 2=Sand | 3=Mud | 4=Organic | 5=Vegetated | |- ML=Moss-Lichen 1=Moss | 2=Lichen
| P=PALUSTRINE----------------------|- EM=Emergent 1=Persistent | 2=Nonpersistent | |- SS=Scrub-Shrub 1=Broad-Leaved | Deciduous | 2=Needle-Leaved | Deciduous | 3=Broad-Leaved | Evergreen | 4=Needle-Leaved | Evergreen | 5=Dead | 6=Indeterminate | Deciduous | 7=Indeterminate | Evergreen | |- FO=Forested 1=Broad-Leaved | Deciduous | 2=Needle-Leaved | Deciduous | 3=Broad-Leaved | Evergreen | 4=Needle-Leaved | Evergreen | 5=Dead | 6=Indeterminate | Deciduous | 7=Indeterminate | Evergreen | |- OW=Open Water/Unknown Bottom (used on older maps) MODIFIERS |- A=Temporarily Flooded |- B=Saturated |- C=Seasonally Flooded |- D=Seasonally Flooded/Well Drained |- E=Seasonally Flooded/Saturated |- F=Semipermanently Flooded |--Non-Tidal------|- G=Intermittently Exposed | |- H=Permanently Flooded | |- J=Intermittently Flooded | |- K=Artificially Flooded | |- W=Intermittently Flooded/Temporary (used on | | older maps) | |- Y=Saturated/Semipermanent/Seasonal (used on | | older maps) | |- Z=Intermittently Exposed/Permanent (used on | | older maps) WATER REGIME----| |- U=Unknown | | | | | |- K=Artificially Flooded | |- L=Subtidal | |- M=Irregularly Exposed | |- N=Regularly Flooded |--Tidal----------|- P=Irregularly Flooded |-*S=Temporary-Tidal |-*R=Seasonal-Tidal |-*T=Semipermanent-Tidal |-*V=Permanent-Tidal |- U=Unknown | |-*These water regimes are only used in | tidally influenced, freshwater systems. |- 1=Hyperhaline |- 2=Euhaline |--Coastal |- 3=Mixohaline (Brackish) | Halinity-------|- 4-Polyhaline | |- 5=Mesohaline | |- 6=Oligohaline | |- 0=Fresh | | | WATER CHEMISTRY-| | |- 7=Hypersaline |--Inland |- 8=Eusaline | Salinity-------|- 9=Mixosaline | |- 0=Fresh | | | | |--pH Modifiers |- a=Acid for all |- t=Circumneutral Fresh Water----|- i=Alkaline SOIL------------------------------|- g=Organic |- n=Mineral |- b=Beaver |- d=Partially Drained/Ditched SPECIAL MODIFIERS-----------------|- f=Farmed |- h=Diked/Impounded |- r=Artificial Substrate |- s=Spoil |- x=Excavated U = Uplands
Note: users of the Wetlands Mapper map service can obtain classification codes by using the Wetland Code Interpreter (yellow button) or users can optionally use this online database search form
Source: http://www.nwi.fws.gov/bd4/other/maps/mapcode.txt
To download NWI data see http://www.nwi.fws.gov/downloads.htm
See also http://www.fws.gov/data/datafws.html