Home Archived December 11, 2018

The USGS Land Cover Institute (LCI)

Frequently Asked Questions (FAQ)

What is the preferred citation when using the National Land Cover Database 1992?

    Vogelmann, J.E., S.M. Howard, L. Yang, C. R. Larson, B. K. Wylie, and J. N. Van Driel, 2001, Completion of the 1990’s National Land Cover Data Set for the conterminous United States, Photogrammetric Engineering and Remote Sensing 67:650-662.

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What is the preferred citation for the National Land Cover 2001 Dataset?

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What is the preferred citation for the NLCD 1992-2001 Land Cover Retrofit Change Product?

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How do I open the Global Land Cover dataset which has a file extension of *.img?
The procedure for importing these raster image files into ArcInfo is as follows:

    1. Rename the image file to filename.bsq.
    2. Prepare an ascii file, named filename.hdr using notepad or wordpad. The file should look something like the following example .hdr file, except the number rows and columns and the x and y coordinates will vary according to the image data. Those image parameters can be found in the documentation for each of the continental databases.

        ulxmap -987549.963

    3. Use the IMAGEGRID command to create a grid file from the image data. Use PROJECTDEFINE to attach the appropriate projection information to the grid. The documentation for each continental database contains the required projection information.
    4. Further information can be found in the ArcInfo help pages under:
      • Heading: Cartography
      • Subhead: Image integration
      • Subhead: BIL, BIP and BSQ data

      • 1 This is not an endorsement of the ArcInfo software.

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I have downloaded the NLCD1992 data and loaded it into ArcMap. Once loaded in, the layer is displayed properly, however, when I open the attribute table the values make no sense and are not in any form of the 21 land use classifications displayed on the website. The attribute tables headings are: ObjectID, Value, Red, Green and Blue. I am unable to do any analysis with the data because whenever I attempt to perform spatial analysis functions (such as raster calculator, or zonal statistics), it does not return results because the land use classifications are not being used in the analysis. However, when I click on the layer for information at one spot, it shows “color value: __” and displays the land use classification. How do I make it so this data is usable in my analysis?

    The NLCD1992 land cover map of Virginia you have downloaded is only a .tif file. ArcMap thus only 'sees' the file as just a picture with no spectral attributes, even though there are. You have to convert your file into an 8bit flat binary file. The instructions on how to do this are located on the LCI website at the following URL. faq_importing_arc.php In short you must first convert your .tif file into a readable binary file that the software package can recognize. This can be done through a software package such as ERDAS Imagine or ENVI. A text header file must also be created and saved with the same name and in the same location as your land cover map file. It will have a subscript .bil or .hdr. In order to bring in the land cover attribute descriptions, you must manually type in the classes by editing the label column found under ATTRIBUTES , LAYER PROPERTIES then click on UNIQUE VALUES. Here you may also remove the black or zero values so you have a neat legend with the 21 land cover classification.

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Is is going to be possible to directly compare land cover from NLCD92 with land cover from NLCD01?

    Direct comparison is not recommended. Each data set was mapped with different methods and slightly different classes. While the two NLCD products are designed to be similar, the slight differences in classification, combined with the final accuracy of the mapping (from 70-80%), result in two distinct products. The typical result of direct comparison will result in a change map showing differences between mapping methods rather than real change on the ground. The NLCD mapping team is completing a product that highlights areas of potential change between the two eras of land cover using the original TM imagery. This product will soon be available on the web site for areas of completed landcover.

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I am looking for formal, detailed metadata for the 2001 NLCD on http://www.mrlc.gov/index.asp but can't seem to find it. Can you point me in the right direction?

    National Land Cover Dataset 2001 (NLCD 2001) mapping zone-level metadata is supplied with all product downloads; standard formats including HTML, XML and TXT are offered. There is currently no provision to provide NLCD 2001 metadata in any other fashion. The NLCD 2001 product set is available via web-enabled file download from the Multi-Resolution Land Characteristics Consortium website: www.mrlc.gov with both Dynamic Download (user defined download areas) and FTP Download (zonal groupings) options offered. The files are available in GeoTIFF, ArcGRID, or BIL formats in most cases; however, the FTP Zonal Area groupings are limited to IMG format.

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I just downloaded both the 1992 and 2001 National Land Cover Dataset land cover maps. I was hoping to use one or the other to quantify land use types in a specific region via ArcMap. Is there any way to go about doing this (ArcMap is not recognizing the image file as something that can be selected)?

    In order to do any data manipulation the data have to be in an ArcGrid format; you have two options:
    1. You can directly download NLCD 2001 in ArcGRID format using the Dynamic Download option (ArcGRID, BIL, GeoTIFF format options) rather than the FTP Download option (IMG format only) if your area of interest isn't too large. A caution is to be careful when making dataset and format option selections so you end up with what you are expecting.
    2. You can convert IMG to ArcGRID in ArcMAP using Spatial Analyst > Raster Calculator > Evaluate > then right click on the file name (calculation temp file)> Make Permanent (you'll be asked where to put it and a name; will produce GRID w/INFO file).

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Has/ is there an accuracy assessment of the National Land Cover Dataset 2001?

    An accuracy assessment of the NLCD 2001 is currently being implemented. A highlight article in the Journal of the American Society for Photogrammetry & remote Sensing (ASPRS) briefly discusses the accuracy of the NLCD 01 product.

    Access the ASPRS article.

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