The National Map Seamless Server, Earth Resources Observation and Science (EROS)
National Land Cover Data (NLCD) Set FAQ
Q. What was the motivation for the creation of the National Land Cover Data Set? A. Many federal agencies, including the U.S. Geological Survey, the U.S. Environmental Protection Agency, the U.S. Forest Service, the National Oceanic and Atmospheric Administration, state goverments, and various environmental groups need up-to-date intermediate scale land cover data. The most recent intermediate scale land cover data set generated for the conterminous United States was developed by the USGS in the 1970's. Although this data set is probably still adequate for some applications, many land cover changes have occurred since the data set was compiled. The main objective of this project is to generate a relatively current, consistent, seamless, and accurate land cover data set for the conterminous United States.Q. Why is land cover data needed, i.e., what are the applications? A. Potential uses of land cover data are many and varied, and include assessing ecosystem status and health, modeling nutrient and pesticide runoff, understanding spatial patterns of biodiversity, land use planning, deriving landscape pattern metrics, and developing land management policy.Q. What is NLCD 1992? A. NLCD 92 (National Land Cover Data 1992) is a 21-category land cover classification scheme that has been applied consistently over the conterminous U.S. It is based primarily on the unsupervised classification of Landsat TM (Thematic Mapper) 1992 imagery. Ancillary data sources included topography, census, agricultural statistics, soil characteristics, other land cover maps, and wetlands data. The NLCD 92 classification is provided as raster data with a spatial resolution of 30 meters.Q. What is NLCD 2001? A. NLCD 2001 is a Landsat based landcover database with several independent data layers, which allow users a wide variety of potential applications. Primary components in the database include:
The National Land Cover Characterization 2001 (NLCD 2001) database is being compiled across all 50 states and Puerto Rico as a cooperative mapping effort of the MRLC 2001 Consortium. This database is being developed using a mapping zone approach, with 65 zones in the continental U.S. and 23 zones in Alaska. The mapping zones outline can be found at: http://www.mrlc.gov/mrlc2k_nlcd.asp Q. What are the classifications of NLCD 1992? A. The NLCD 1992 21 Land Cover Classifications definition are at: http://landcover.usgs.gov/classes.phpQ. What are the classifications of NLCD 2001? A. The NLCD 2001 Land Cover Classifications definitions are at: http://www.mrlc.gov/nlcd_definitions.asp Q. What are the difference between NLCD 1992 and NLCD 2001? A. The main difference is the dates of the source data. Just like the name implies, NLCD 1992 was taken from 1992 vintage imagery and NLCD 2001 was taken from the MRLC 2001 project. More products are provided with the NLCD 2001 data. NLCD 1992 only product is Land Cover. NLCD 2001 provides Land Cover, Impervious, and Canopy data. Q. What products are available for NLCD 2001? A. Land Cover refers to the classification of the land using the land cover definitions mentioned previously. Impervious surfaces refers to impenetrable surfaces such as rooftops, roads, or parking lots. Tree canopy refers a layer or multiple layers of branches and foliage at the top or crown of a forest's trees. The standardized nature of each data component can allow users the ability to develop data applications that use layers either synergistically or individually. For example, imperviousness can potentially be used not only as a way to classify developed land, but also in water run-off models, green space calculations, and urban planning scenarios. Tree canopy can be intersected with NLCD 2001 forest classes to provide canopy categories by density. Further, the consistency of these data layers will allow direct comparison from place to place across the Nation increasing the utility of potential applications. Q. What is the coverage area of NLCD 1992? A. The coverage are for NLCD 1992 is the conterminous United States. Q. What is the status and coverage area of NLCD 2001? A. The National Land Cover Characterization 2001 (NLCD 2001) database is being compiled across all 50 states and Puerto Rico as a cooperative mapping effort of the MRLC 2001 Consortium. A status map can be found at: http://www.mrlc.gov/mrlc2k_nlcd.asp To see availabilty of the data on The National Map Seamless Server:
Q. What are the specifications for NLCD 1992 and NLCD 2001? A.
Q. What formats are available? A. There are 3 formats available: ArcGrid is an Arc/Info proprietary format. Some other software packages can read the ArcGrid format. Customers who specify ArcGrid will be delivered a workspace. The workspace is not tarred or gzipped. BIL is a non-proprietary format made by running the GRIDIMAGE command in Arc. The data is a simple binary raster format (signed integer data). There is an accompanying ASCII header file that provides file size information (number of rows and columns). The data are stored in row major order (all the data for row 1, followed by all the data for row 2, etc.). TIFF with world file for NLCD is a non-proprietary format. It is essentially a floating-point binary data file with accompanying ASCII descriptor files including a world file containing geographic extents for the file. Q. Where can more information be found concerning the NLCD program? A. More information can be found a the MRLC homepage, http://www.mrlc.gov/mrlc2k_nlcd.asp From this site, there are links to descriptions, papers, references, and partners information. Also, information concerning other Land Cover projects can be found at: http://landcover.usgs.gov There is also a Land Cover email address for more technical questions. lcac@usgs.gov Q. Is there a NLCD 2001 factsheet? A. Yes, the link is http://www.mrlc.gov/includes/nlcd_fact_sheet_2001.pdf |
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://seamless.usgs.gov/faq/nlcd_faq.php
Page Contact Information: webmapping@usgs.gov
Page Last Modified: March 06, 2008
