NLCD Land Cover Class Definitions
(http://landcover.usgs.gov/classes.asp)

The classification system used for NLCD is modified from the Anderson 
land-use and land-cover classification system. Many of the Anderson 
classes, especially the Level III classes, are best derived using aerial 
photography. It is not appropriate to attempt to derive some of these 
classes using Landsat TM data due to issues of spatial resolution and 
interpretability of data. Thus, no attempt was made to derive classes 
that were extremely difficult or impractical to obtain using 
Landsat TM data, such as the Level III urban classes. In addition, some 
Anderson Level II classes were consolidated into a single NLCD class. 

Water
11 Open Water
12 Perennial Ice/Snow 

Developed
21 Low Intensity Residential
22 High Intensity Residential
23 Commercial/Industrial/Transportation 

Barren
31 Bare Rock/Sand/Clay
32 Quarries/Strip Mines/Gravel Pits
33 Transitional 

Forested Upland 
41 Deciduous Forest
42 Evergreen Forest
43 Mixed Forest 

Shrubland
51 Shrubland

Non-Natural Woody
61 Orchards/Vineyards/Other 

Herbaceous Upland Natural/Semi-natural Vegetation
71 Grasslands/Herbaceous 

Herbaceous Planted/Cultivated
81 Pasture/Hay
82 Row Crops
83 Small Grains
84 Fallow
85 Urban/Recreational Grasses 

Wetlands
91 Woody Wetlands
92 Emergent Herbaceous Wetlands

Expanded definitions:

Water - All areas of open water or permanent ice/snow cover.
11. Open Water - all areas of open water, generally with less than 25% 
    cover of vegetation/land cover. 
12. Perennial Ice/Snow - all areas characterized by year-long surface 
    cover of ice and/or snow. 

Developed Areas -  characterized by a high percentage (30 percent or greater) 
of constructed materials (e.g. asphalt, concrete, buildings, etc).
21. Low Intensity Residential - Includes areas with a mixture of constructed 
    materials and vegetation.  Constructed materials account for 30-80 percent 
    of the cover. Vegetation may account for 20 to 70 percent of the cover. 
    These areas most commonly include single-family housing units. Population 
    densities will be lower than in high intensity residential areas.
22. High Intensity Residential - Includes highly developed areas where people 
    reside in high numbers. Examples include apartment complexes and row 
    houses.  Vegetation accounts for less than 20 percent of the cover. 
    Constructed materials account for 80 to100 percent of the cover.
23. Commercial/Industrial/Transportation - Includes infrastructure (e.g. 
    roads, railroads, etc.) and all highly developed areas not classified as 
    High Intensity Residential.

Barren - Areas characterized by bare rock, gravel, sand, silt, clay, or other 
earthen material, with little or no "green" vegetation present regardless of 
its inherent ability to support life. Vegetation, if present, is more widely 
spaced and scrubby than that in the "green" vegetated categories; lichen cover 
may be extensive. 
31. Bare Rock/Sand/Clay - Perennially barren areas of bedrock, desert 
    pavement, scarps, talus, slides, volcanic material, glacial debris, beaches,
    and other accumulations of earthen material.
32. Quarries/Strip Mines/Gravel Pits - Areas of extractive mining activities 
    with significant surface expression.
33. Transitional - Areas of sparse vegetative cover (less than 25 percent of 
    cover) that are dynamically changing from one land cover to another, often 
    because of land use activities. Examples include forest clearcuts, a 
    transition phase between forest and agricultural land, the temporary 
    clearing of vegetation, and changes due to natural causes (e.g.  fire, 
    flood, etc.).

Forested Upland - Areas characterized by tree cover (natural or semi-natural 
woody vegetation, generally greater than 6 meters tall); tree canopy accounts 
for 25-100 percent of the cover.
41. Deciduous Forest - Areas dominated by trees where 75 percent or more of 
    the tree species shed foliage simultaneously in response to seasonal change.
42. Evergreen Forest - Areas dominated by trees where 75 percent or more of 
    the tree species `maintain their leaves all year. Canopy is never without 
    green foliage.
43. Mixed Forest - Areas dominated by trees where neither deciduous nor 
    evergreen species represent more than 75 percent of the cover present. 

Shrubland - Areas characterized by natural or semi-natural woody vegetation 
with aerial stems, generally less than 6 meters tall, with individuals or 
clumps not touching to interlocking. Both evergreen and deciduous species of 
true shrubs, young trees, and trees or shrubs that are small or stunted 
because of environmental conditions are included.
51. Shrubland - Areas dominated by shrubs; shrub canopy accounts for 25-100 
    percent of the cover. Shrub cover is generally greater than 25 percent 
    when tree cover is less than 25 percent. Shrub cover may be less than 25 
    percent in cases when the cover of other life forms (e.g. herbaceous or 
    tree) is less than 25 percent and shrubs cover exceeds the cover of the 
    other life forms.

Non-Natural Woody - Areas dominated by non-natural woody vegetation; 
non-natural woody vegetative canopy accounts for 25-100 percent of the cover. 
The non-natural woody classification is subject to the availability of 
sufficient ancillary data to differentiate non- natural woody vegetation from 
natural woody vegetation. 
61. Orchards/Vineyards/Other - Orchards, vineyards, and other areas planted 
    or maintained for the production of fruits, nuts, berries, or ornamentals. 

Herbaceous Upland - Upland areas characterized by natural or semi-natural 
herbaceous vegetation; herbaceous vegetation accounts for 75-100 percent of 
the cover.
71. Grasslands/Herbaceous - Areas dominated by upland grasses and forbs. 
    In rare cases, herbaceous cover is less than 25 percent, but exceeds the 
    combined cover of the woody species present. These areas are not subject 
    to intensive management, but they are often utilized for grazing.

Planted/Cultivated - Areas characterized by herbaceous vegetation that has 
been planted or is intensively managed for the production of food, feed, or 
fiber; or is maintained in developed settings for specific purposes. 
Herbaceous vegetation accounts for 75-100 percent of the cover. 
81. Pasture/Hay - Areas of grasses, legumes, or grass-legume mixtures 
    planted for livestock grazing or the production of seed or hay crops.
82. Row Crops - Areas used for the production of crops, such as corn, 
    soybeans, vegetables, tobacco, and cotton. 
83. Small Grains - Areas used for the production of graminoid crops such as 
    wheat, barley, oats, and rice.
84. Fallow - Areas used for the production of crops that do not exhibit 
    visible vegetation as a result of being tilled in a management practice 
    that incorporates prescribed alternation between cropping and tillage.
85. Urban/Recreational Grasses - Vegetation (primarily grasses) planted in 
    developed settings for recreation, erosion control, or aesthetic purposes. 
    Examples include parks, lawns, golf courses, airport grasses, and 
    industrial site grasses. 

Wetlands - Areas where the soil or substrate is periodically saturated with 
or covered with water as defined by Cowardin et al.
91. Woody Wetlands - Areas where forest or shrubland vegetation accounts for 
    25-100 percent of the cover and the soil or substrate is periodically 
    saturated with or covered with water.
92. Emergent Herbaceous Wetlands - Areas where perennial herbaceous vegetation 
    accounts for 75-100 percent of the cover and the soil or substrate is 
    periodically saturated with or covered with water. 

Reference:  Cowardin, L.M., V. Carter, F.C.  Golet, and E.T. LaRoe, 1979. 
                     Classification of Wetlands and Deepwater 
                     Habitat of the United States, Fish and Wildlife 
                     Service, U.S. Department of the Interior, Washington, D.C.