Has an accuracy been completed for the NLCD 2001 land cover product?

Yes, an accuracy assessment was completed. The article citation is Wickham, J. D., S. V. Stehman, J. A. Fry, J. H. Smith, and C. G. Homer. 2010. Thematic accuracy of the NLCD 2001 land cover for the conterminous United States. Remote Sensing of Environment 114 (6):1286-1296.

Why is it taking so long for me to download the NLCD 2006 land cover product?

The NLCD2006 land cover product is currently only available in one file size and includes all lower 48 U.S. States. The NLCD2006 land cover product is 1.1 Gb zipped, and extracts to approximately 17 Gb. The NLCD2006 products are also available for download by user defined area from the MRLC Consortium Viewer. (max download file size is 250Mb).

Why am I unable to successfully unzip the NLCD 2006 land cover product?

Depending on which zip file software you are using it might be restricted to only a 4Gb data file size limit. The NLCD2006 land cover product is 1.1 Gb zipped and approximately 17 Gb unzipped. Although we do not endorse any specific zip file software to use with our data we have found that other users have had the most success un-zipping the NLCD2006 land cover file with WinZip and/or 7-Zip software.

Are the NLCD 2006 Land Cover and Percent Developed Impervious Surface Products available in smaller file sizes?

The NLCD2006 land cover and percent developed impervious surface products are available from the MRLC Consortium Viewer. (max download file size is 250Mb).

I am unable to work with such a large dataset on my computer. Is there a method I can use to make the NLCD 2006 land cover product a more manageable size until it becomes available on the MRLC Consortium Viewer?

For a short term fix we recommend the following procedure for ArcMap and ERDAS Imagine users.

ArcMap

1. Start ArcCatalog.
2. Right-click in the folder where your NLCD 2006 land cover raster layer is located and select New > Shapefile.
3. Name the new Shapefile e.g., NLCD_06_Clip and specify:
   a. Feature Type = POLYGON
   b. Spatial Reference > Edit > Import a coordinate system and select the NLCD2006_landcover raster layer.
4. Start a new session of ArcMap.
5. Add the new Shapefile layer and the NLCD 2006 land cover raster layer.
6. Click Editor > Start Editing and Specify:
   a. Task = Create New Feature
   b. Target = Shapefile you created in Step #2
7. Select the Create New Feature tool.
8. Draw a polygon around the area of interest on the NLCD 2006 land cover raster layer.
9. Stop editing and save your edits.
10. Right Click on the NLCD 2006 land cover raster layer.
11. Select Data > Export Data and choose the following options:
    a. Extent = Data Frame (Current)
    b. Spatial Reference = Raster Dataset (Original)
    c. Rename the file name and select a desired output file format
    d. Click Save
    
12. Click YES to add the exported data to the map as a layer.

ERDAS IMAGINE

1. Open a new viewer and load the NLCD 2006 land cover raster layer.
2. In the viewer with the NLCD 2006 land cover select from the menu AOI > Tools and draw an area of interest on the NLCD 2006 land cover raster.
3. Make sure the AOI is complete (i.e., a complete polygon) and selected.
4. Go to DataPrep > Subset image and select the following options:
   a. Input File = NLCD 2006 land cover raster layer
   b. Output File = provide a name for your clipped NLCD 2006 land cover raster layer
   c. Click AOI > Source is Viewer
   d. Click OK twice
   
5. Add the clipped NLCD 2006 land cover raster layer.

Can I use the NLCD 2001 Version 1.0 land cover and percent developed impervious products with the NLCD 2006 land cover and percent developed impervious products?

No, you will need to download the NLCD 2001 Version 2.0 land cover and percent developed impervious products. There is no NLCD 2001 Version 2.0 for percent canopy.

What is the preferred citation for the National Land Cover 1992 Database?

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.

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

Homer, C. C. Huang, L. Yang, B. Wylie and M. Coan. 2004. Development of a 2001 National Landcover Database for the United States. Photogrammetric Engineering and Remote Sensing*, Vol. 70, No. 7, July 2004, pp. 829-840.

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

Fry, J.A., Coan, M.J., Homer, C.G., Meyer, D.K., and Wickham, J.D., 2009, Completion of the National Land Cover Database (NLCD) 1992–2001 Land Cover Change Retrofit product: U.S. Geological Survey Open-File Report 2008–1379, 18 p.

What if I think an area has the wrong land cover classification?

First, make sure you are interpreting the land cover class definitions correctly. Pay special attention to the % cover thresholds that discriminate the class. For example, a shrub land with a 15% tree over story is still considered a shrubland. It is not until the tree over story reaches 20% that it should be classified as a forest class. Second, remember the minimum mapping unit of NLCD is about 1 acre, so if a feature is smaller then 1 acre it is not captured. Third, remember that NLCD is a national mapping effort done at a regional scale, meaning if your local patch of land cover is unique or uncharacteristic of the surrounding area, chances are higher it cannot be captured appropriately at the regional scale of the mapping.

Should I directly compare land cover from NLCD 92 with land cover from NLCD 2001?

Direct comparison is not recommended. Each dataset 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 has completed a product that highlights areas of potential change between the two eras of land cover using the original TM imagery. This product is available for download at the MRLC web site. Access the Retrofit Land Cover Change Data product.