National Land Cover Database (NLCD) Tiled Data Distribution SYstem (TDDS) Zipfile Content Readme

Table of Contents


INTRODUCTION
Process Description
Part 1: Data Specification
PART 2: TILED DATA DISTRIBUTION SYSTEM (TDDS) - ORTHOIMAGERY INFORMATION
Part 3: FILE NAMING CONVENTION
PART 4: CONTENTS OF ZIPFILE
PART 5: DISTRIBUTION INFORMATION
Part 6: Resource Information

Introduction
The National Land Cover Database 2001 Land Cover 2011 Edition layer is produced through a cooperative project conducted by the Multi-Resolution Land Characteristics (MRLC) Consortium.  The MRLC Consortium is a partnership of federal agencies (www.mrlc.gov), consisting of the U.S. Geological Survey (USGS), the National Oceanic and Atmospheric Administration (NOAA), the U.S. Environmental Protection Agency (EPA), the U.S. Department of Agriculture (USDA), the U.S. Forest Service (USFS), the National Park Service (NPS), the U.S. Fish and Wildlife Service (FWS), the Bureau of Land Management (BLM) and the USDA Natural Resources Conservation Service (NRCS).  One of the primary goals of the project is to generate a current, consistent, seamless, and accurate National Land cover Database (NLCD) circa 2001 for the United States at medium spatial resolution.  This land cover map and all documents pertaining to it are considered "provisional" until a formal accuracy assessment can be conducted.  For a detailed definition and discussion on MRLC and the NLCD 2001 products, refer to Homer et al. (2004) and http://www.mrlc.gov/mrlc2k.asp.

      The NLCD 2001 is created by partitioning the U.S. into mapping zones.  A total of 66 mapping zones were delineated within the conterminous U.S. based on ecoregion and geographical characteristics, edge matching features and the size requirement of Landsat mosaics.  This update represents a seamless assembly of updated NLCD 2001 Land Cover (2011 Edition) for all 66 MRLC mapping zones.  Questions about the NLCD the NLCD 2001 Land Cover 2011 Edition can be directed to the NLCD 2001 land cover mapping team at the USGS/EROS, Sioux Falls, SD (605) 594-6151 or mrlc@usgs.gov.


Process Description
 The land cover classification was achieved by use of a classification and decision tree method (DT) using a combination of Landsat imagery and ancillary data. The specific DT program employed is called C5, which implements a gain ratio criterion in tree development and pruning (Quinlan, 1993).  C5 also implemented several advanced features that can aid and improve land cover classification, including boosting and cross-validation.  Boosting is a technique for improving classification accuracy, while cross-validation can provide certain level of estimation regarding the land cover classification quality.  In addition, C5 can generate a confidence estimate for each classified pixel and record the associated classification logic in a text file that can be readily interpreted and incorporated into a metadata system.

        To conduct the land cover classification using DT, a large quantity of training data is required. For the NLCD 2001 Land Cover, training data were collected from several combined sources.

        Note that the training data were used to map all land cover classes except for four classes in urban and sub-urban areas (developed open space, low intensity developed, medium intensity developed, high intensity developed).  All urban and suburban land cover classes were mapped and quality assessed separately through a sub-pixel quantification of impervious surfaces using a regression tree modeling method.

        Following the development of the best classification through decision tree modeling, additional steps were required to complete the final land cover product.  The four classes in urban and suburban areas were determined from the percent imperviousness mapping product (described in the next section).  The threshold for the four classes is: (1) developed open space (imperviousness < 20%), (2) low-intensity developed (imperviousness from 20 - 49%), (3) medium intensity developed (imperviousness from 50 -79%), and (4) high-intensity developed (imperviousness > 79%).  Other classes of forest and non-forest were combined with the urban classes to complete the land cover product.  Finally visual inspection of the classification was made with areas/pixels that were wrongly classified delineated first as an "area of interest" (AOI), subsequently then limited manual editing was done to eliminate the classification error within the AOI.

        The completed single pixel product was then generalized to a 1 acre (approximately 5 ETM+ 30 m pixel patch) minimum mapping unit product using a "smart eliminate" algorithm. This aggregation program subsumes pixels from the single pixel level to a 5-pixel patch using a queens algorithm at doubling intervals. The algorithm consults a weighting matrix to guide merging of cover types by similarity, resulting in a product that preserves land cover logic as much as possible.
        For Landsat Scene Acquisition dates and identification numbers for imagery used in the NLCD 2001 land, please see:  appendix2_nlcd2001_scene_list_by_zone.txt

        Landsat data and ancillary data used for the land cover prediction -

        Data Type of DEM composed of 1 band of Continuous Variable Type.

        Data Type of Slope composed of 1 band of Continuous Variable Type.

        Data Type of Aspect composed of 1 band of Categorical Variable Type.

        Data type of Position Index composed of 1 band of Continuous Variable Type.

Process Step for NLCD 2001 Land Cover (2011 Edition)
        To improve NLCD imperviousness the 2011 project included a process to reduce omission and commission error in NLCD 2001, 2006, and 2011 products.  This activity was completed for urban areas in most of the eastern ½ of the conterminous United States.  High resolution (one-meter ground sample distance) National Aerial Imagery Program (NAIP – http://fsa.usda.gov/FSA/) imagery was used to verify imperviousness.  Using hand-edits imperviousness was removed from areas incorrectly identified as developed and added to areas where developed land cover was missed.  A modeling process was implemented to parse imperviousness changes to the correct era.  These improvements were incorporated with the derived developed classes in all areas of imperviousness and land cover versions released with NLCD 2011 editions.

PART 1: Data Specifications and Products


	Resolution:      	one Arc Second (~30 meter)
  	Data type:      	GeoTIFF
  	Projection:  		Albers Conical Equal Area
  	Datum:       		NAD83
  	

	NLCD 2001 - Landcover  - 2011 Edition includes data for Conterminous U.S..  
	

PART 2: TILED DATA DISTRIBUTION SYSTEM (TDDS) - NLCD INFORMATION

Tiled Data Distribution System (TDDS) is a means to access pre-packaged data.  Each 2001 NLCD product are cut to 3 x 3 degree tiles and zipped for online download.  The zip bundles contain the product image and associated files, an overall coverage shapefile, metadata, color table file, appendix of scene listings, and readme.  The data is available for download thru The National Map viewer and MRLC viewer.  (http://viewer.nationalmap.gov/viewer/ and http://gisdata.usgs.gov/website/mrlc/viewer.htm)

Part 3: FILE NAMING CONVENTION

Each tile is cut to a 3 x 3 degree area.  The naming convention for each tile is the NLCD product and lower right corner coordinate. 


The file naming convention is:
	
        NLCDFFFF_NNN_aaaaaa

		NLCD      =  National Land Cover Database
		FFFF      =  Project Year (2001)
                NNN       =  Product type (LC = Landcover, IMP = Imperviousness
		aaaaaa    =  Lower right corner coordinate (N24W078) 		


  	Example: NLCD2001_LC_N24W078.zip 

			NLCD     =  National Land Cover Database
	 		2001     =  Project year 2001
		      	LC       =  Landcover product
                        N24W078  =  Tile extent starts at the lower right corner coodinate of N 					24 and W 78. The data covers an area within N 24, N 27, 
					W 78, W 81  
                        			           

PART 4: CONTENTS OF ZIPFILE

	
	.tif  	 =  Geotiff image
	.tfw	 =  World file for full resolution Geotiff image
	.aux.xm l=  diplay info
	.prj	 =  Projection File
	.jpg	 =  Lossy compressed image
	.jpw     =  World file for lossy compressed image
	.xml     =  FGDC Metadata file 
	.htm     =  HTML format FGDC metadata file suitable for reading and printing
	.vat.dbf =  Color table information
	Shapefile
	 (.dbf, .prj, .sbn, .sbx, .shp, .shx)
		=  The shapefile (consisting of 6 files) represents the overall 3 x 3 degree GRID 
	NLCDReadme2001_LC_2011Edition.txt 
		=  The readme text file
	Appendix
		=  List of Landsat scenes and scene dates by path/row used in this project


PART 5: DISTRIBUTION INFORMATION

	Access points (i.e. map interface) can be found at:
		
		http://viewer.nationalmap.gov/viewer/ and http://gisdata.usgs.gov/website/mrlc/viewer.htm
	
	To acquire entire datasets via Bulk Data Distribution, they can be found at:
	
		http://www.mrlc.gov/


Part 6: Resource Information

Information concerning the Multi-Resolution Land Characteristics Consortium  (MRLC), data info, and refernces can be found at:
	
		http://www.mrlc.gov/



Disclaimer:  Any use of trade, product, or firm names is for descriptive 
purposes only and does not imply endorsement by the U. S. Government.    


Readme Publication Date:  May 2014


