The goal of the Gap Analysis Program National Land Cover data is to provide accurate, seamless, data on the vegetation of the United States. These data map vegetation using NatureServe’s ecological system classification scheme. This detailed classification system provides information on vegetation types at a community level. Vegetation data at this level of detail can provide information on wildlife habitat distribution patterns, provide information for conservation assessments and can serve as input into models predicting hydrologic, fire and climatic processes. The GAP National Land Cover data also provide a crosswalk from Ecological Systems to the five highest levels of the National Vegetation Classification System (NVC) allowing users to display the data at six levels of thematic detail.
Strategy show details
The original GAP land cover products were completed at the state level, with each state having the responsibility of implementing a project design for the geographic area within their state boundaries. These early projects were often among the first land cover mapping projects in a state and resulted in much forward progress in land cover mapping techniques. However, a lack of standardized methods and classification schemes between states made regional analysis using these products difficult.
To overcome the problem of inconsistency between states, the second generation of GAP land cover maps was conducted at the regional scale (between five and nine states). The first regional project was completed in the Southwest in 2005 , the second in the Southeast in 2007, and the Northwest and California were completed in 2009. All three region land cover data products used 1999-2001 Landsat ETM+ satellite imagery as a base and are classified using NatureServe’s Ecological System, and used similar modeling techniques. This consistency allowed the regional GAP products to be pulled together into a seamless dataset. For areas of the country where a regional GAP product had not been completed (Midwest, Northeast and Alaska), data from the Landfire project was used. This combination of products was feasible because of the comparable imagery, classification system, and modeling techniques used by the Landfire project.
The Gap Analysis Program is currently working, in coordination with Landfire, to develop a strategy for updating the National Land cover data. Having a time series of detailed vegetation data available would allow for analysis of vegetation changes over time, which would be valuable to studies on global climate change, fire dynamics, and wildlife management.
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Current Status show details
Land cover data derived from 1999-2001 Landsat data is currently available as 30 meter resolution raster data for the Continental U. S., Alaska and Hawaii, through the GAP land cover viewer. Land cover data has recently been completed for the U. S. Virgin Islands and Puerto Rico. The U.S. Virgin Island and Puerto Rico data have not yet been integrated into the viewer, but they are available for download.
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U.S. Department of the Interior |
U.S. Geological Survey