**  Comparison of Land Cover Datasets NLCD and WV-GAP **

Both land cover datasets (WV-GAP and NLCD) were originally created from classified Landsat TM imagery that was purchased as part of the Multi-Resolution Land Characteristics Consortium (MRLC) program.   MRLC is an interagency effort to map land cover (EPA, USGS etc). The first MRLC land cover product was land cover for EPA region 3, which includes WV.  The WV MRLC land cover was completed several years ago, and has been modified slightly since then.

The NLCD program is now distributing MRLC land cover data.  MRLC/NLCD land cover data is now complete for almost all states.

You can download MRLC/NLCD land cover from:
http://edcwww.cr.usgs.gov/pub/edcuser/vogel/states/

The data sets (MRLC/NLCD and WV-GAP) differ largely because of the original goals in creating the land cover datasets.  MRLC/NLCD data were created to provide a somewhat standard Anderson level II land cover dataset for the entire country.  WV-GAP land cover data were created as an input to wildlife species distribution modeling in WV based on wildlife habitat types.

Important differences between the WV-GAP land cover and the MRLC/NLCD data include:

WV-GAP used both leaf-on and leaf-off TM scenes for classification.  The read me file for WV MRLC/NLCD data indicates that they used leaf-off data, but only as ancillary data.  WV-GAP used both leaf-on & leaf-off directly in classification.  WV-GAP also used some of the same TM scenes as MRLC/NLCD (most date from 1992-1993) but some slightly newer ones (1994).

The MRLC/NLCD data for WV was not created specifically for WV, but was extracted from the entire EPA region 3 dataset (WV, VA, PA, MD).  The methods used to create the Region 3 land cover dataset by MRLC were different than the methods used by WV-GAP.  Basically, MRLC classified a larger area at once and then clipped the results to the state borders.  They merged their TM scenes together (regardless of date) for the entire region prior to classification, and they used fewer clusters (80).  

For WV-GAP, image classification was performed separately for each TM scene and ecological region (e.g. coalfields, Northern Ridge & Valley). WV-GAP did not merge different TM scenes together, and used more clusters (250).  Once each TM scene/subsection combination was classified, each subsection/scene was merged together to create a land cover map for the entire state.  WV-GAP also used additional ancillary data to aid in image classification, including historic land cover data & 58,000 videography-based sample points.

The MRLC/NLCD data don't include the same land cover classes as WV-GAP data.  MRLC only includes deciduous, coniferous, and mixed for forest types, while WV-GAP includes 8 different forested land cover types.  One of the issues noticed with the MRLC land cover for WV is that it seems to overestimate the area of row crops in the state.


Jacquelyn Strager / Charles Yuill
Natural Resource Analysis Center
West Virginia University
Morgantown, WV  26506-6108
304-293-4832 ext.4455
jrowe@wvu.edu ; cyuill@wvu.edu