The Land Cover Trends classification system used consisted of 11 general LULC classes. The LULC classes paralleled the Anderson Level I classification system (Anderson and others, 1976), but was modified by including two transitional disturbance categories; mechanically disturbed denotes human-induced disturbances and non-mechanically disturbed denotes natural disturbances. The decision to use general, Level I classes was primarily made to achieve high interpretation accuracy and consistency using moderate resolution imagery.
Since Landsat MSS, TM, and ETM+ imagery have limitations on what LULC categories can be correctly identified and/or what land change can be discerned between images, we erred on the side of creating LULC maps at the lower spatial resolution of the Landsat MSS imagery. A minimum mapping unit (MMU) of 60 meters was used for the study. This meant that features with ground footprints less than 60 meters wide, such as narrow roads or low-density development, were not mapped because they fell below the MMU.
Land-use and land-cover classification system used to develop data for the Land Cover Trends dataset
[The classification system is a modified version of the Anderson Level I classification system and consists of the following 11 general classes. * Indicates category included to capture anthropogenic or natural disturbance events.]
Areas persistently covered with water, such as streams, canals, lakes, reservoirs, bays, or oceans.
Areas of intensive use with much of the land covered with structures (e.g., high density residential, commercial, industrial, transportation, mining, confined livestock operations), or less intensive uses where the land cover matrix includes both vegetation and structures (e.g., low density residential, recreational facilities, cemeteries, etc.), including any land functionally attached to the urban or built-up activity.
Land in an altered and often non-vegetated state that, due to disturbances by mechanical means, is in transition from one cover type to another. Mechanical disturbances include forest clear-cutting, earthmoving, scraping, chaining, reservoir drawdown, and other similar human-induced changes.
Land comprised of natural occurrences of soils, sand, or rocks where less than 10% of the area is vegetated.
Areas with extractive mining activities that have a significant surface expression. This includes (to the extent that these features can be detected) mining buildings, quarry pits, overburden, leach, evaporative, tailing, or other related components.
Tree-covered land where the tree-cover density is greater than 10%. Note that cleared forest land (i.e., clear-cut logging) will be mapped according to current cover (e.g., disturbed or transitional, shrubland/grassland).
Land predominately covered with grasses, forbs, or shrubs. The vegetated cover must comprise at least 10% of the area.
Cropland or pastureland in either a vegetated or non-vegetated state used for the production of food and fiber. Note that forest plantations are considered as forests or woodlands regardless of the use of the wood products.
Lands where water saturation is the determining factor in soil characteristics, vegetation types, and animal communities. Wetlands are comprised of water and vegetated cover.
Land in an altered and often non-vegetated state that, due to disturbances by nonmechanical means, is in transition from one cover type to another. Nonmechanical disturbances are caused by wind, floods, fire, animals, and other similar phenomenon.
Land where the accumulation of snow and ice does not completely melt during the summer period.