The GAP national land cover data, based on the NatureServe Ecological Systems Classification, is the most detailed, consistent map of vegetative associations ever available for the United States and will help facilitate the planning and management of biological diversity on a regional and national scale. The Alaska and Continental U.S. portion of the data set contains 680 Ecological systems and 28 land use, introduced vegetation or disturbed classes. The Hawaii data contains 28 natural vegetation classes and nine land use, introduced vegetation or disturbed classes. This data set can be used to identify those places in the country with sufficient good quality habitat to support wildlife, a key step in developing sound conservation plans.
Information about land cover is a key component of effective conservation planning and the management of biological diversity as it is used to build predictive models of wildlife distribution and biodiversity across large geographic areas. The new national data set also provides a consistent method for characterizing land cover, which will facilitate monitoring how that land cover changes over time.
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Land Cover Data Features
The second version of the GAP land cover data combines ecological system data from previous GAP projects in the Southwest, Southeast, and Northwest United States with recently updated California data. For Alaska ,and areas of the continental United States, where ecological system-level GAP data has not yet been developed, data from the LANDFIRE project used. This approach allowed GAP mappers to construct a seamless representation of ecological system distributions across the continental United States and Alaska. In Hawaii, data created by the Hawaii GAP project was used. This data set uses a classification system developed by the project for Hawaii and not the ecological system.
Frequently, this high number of classes provides a level of detail that exceeds a user’s needs. To accommodate these users, we have crosswalked the ecological system level data to the five highest levels of the National Vegetation Classification System( NVC). The vegetation features used to distinguish these classes range from growth form, and climate regimes at the Class level to regional differences in substrate and hydrology at the Macrogroup level (Table 1; http://biology.usgs.gov/npsveg/nvcs.html). The NVC levels provide the user with a variety of options allowing the choice of making a map of the Continental U.S. with eleven classes at the NVC Class level to 583 classes at the Ecological system level.
Features used to delineate National Vegetation Classification (NVC) levels:
- Class
- dominant general growth forms adapted to basic moisture, temperature, and/or substrate or aquatic
- Subclass
- global macroclimatic factors driven primarily by latitude and continental position, or reflect overriding substrate or aquatic conditions
- Formation
- global macroclimatic conditions as modified by altitude, seasonality of precipitation, substrates, hydrological conditions
- Division
- continental differences in mesoclimate, geology, substrates, hydrology, disturbance regimes
- Macrogroup
- sub-continental to regional differences in mesoclimate, geology, substrates, hydrology, disturbance regimes
How to Cite This Data Set
US Geological Survey, Gap Analysis Program (GAP). August 2011. National Land Cover, Version 2.