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Intermediate ArcGIS 9
   Landcover Analysis

Course Introduction
Getting Started
Overview of data
 - MELCD products
 - NLCD products
 - Satellite data
 - Review of legacy data
 - TIFF data format
Spatial Analyses
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NLCD 2001 Products

Concepts:
   NLCD 2001 landcover
   NLCD 2001 landcover - 1995
   NLCD 2001 landcover change - 1995-2001
   NLCD 2001 imperviousness
   NLCD 2001 canopy cover
   thematic resolution
   spatial resolution

The NLCD 2001 project is a national cooperative effort between many federal agencies (chiefly NOAA and USGS) to map landscape features and change consistently for the US.  It arose from earlier circa-1992 efforts to map landcover (USGS' original NLCD project) and coastal changes (NOAA's Coastal Change Assessment Project - CCAP).  The 2001 project varies tremendously from the original projects in several areas:
 - accuracy is greatly improved
 - NLCD 2001 and CCAP 2001 are entirely integrated (we will refer to them combined as just NLCD 2001 for simplicity)
 - many more products are available to the end-user
 - a single consistent mapping system is used for the entire country

The NLCD 2001 products formed the base for the MELCD 2004 products.  The NLCD 2001 products have a greater thematic resolution than the MELCD 2004 products, meaning that they typically use more classes or provide more information about a mapped area.  For example, the NLDC 2001 landcover product depicts seven types of wetlands, whereas the MELCD 2004 landcover only shows two.  However, the trade-off is a lower spatial resolution, meaning that those mapped areas are larger in NLCD 2001 products than MELCD 2004 products.  For example, in all NLCD 2001 products, the pixel size is 30 meters, with a minimum mapping unit of 2 acres.  Compare this to a 5-meter pixel size and .89 acre MMU for the MELCD 2004 products.  Spatial accuracy of the MELCD 2004 products are about 15 meters, while NLCD 2001 products have a spatial accuracy of about 60 meters.  NLCD 2001 products are designed for use over larger areas and smaller scales, such as a maximum scale of roughly 1:100,000 and analyses conducted at the county or watershed level.

Our data covers the NLCD 2001 zone 66, which includes Maine and portions of New Hampshire and Vermont.

NLCD 2001 landcover
The most well-known product of the NLCD 2001 project is the 2001 landcover dataset, with 21 landcover classes in Maine (the full NLCD 2001 classification nationwide includes 5 other classes not found in zone 66); for details see the metadata.  Accuracy is > 80% based on a sample of 697 points, for details see the error matrix.  The classification includes:
Pixel
value   Class
2        Developed, High Intensity  (80-100% impervious)
3        Developed, Medium Intensity  (50-79% impervious)
4        Developed, Low Intensity  (21-49% impervious)
5        Developed, Open Space  (developed areas, but 0-20% impervious - city parks, golf courses, baseball fields, etc.)
6        Cultivated Crop  (production of annual crops such as corn, potatoes, strawberries, and tilled barren fields)
7        Pasture/Hay  (grasses are major vegetation, managed for harvesting as hay or grazing)
8        Grassland/Herbaceous  (unmanaged grasslands - rare in Maine)
9        Deciduous Forest  (> 20% tree canopy cover, > 75% of trees are deciduous)
10      Evergreen Forest  (> 20% tree canopy cover, > 75% of trees are evergreen)
11      Mixed Forest   (> 20% tree canopy cover, 25-75% are deciduous)
12      Scrub/Shrub   (woody vegetation < 5m tall is > 20% of cover - typically regenerating fields, cuts, or rights-of-way)
13      Palustrine Forested Wetland (freshwater wetland with majority tree canopy cover)
14      Palustrine Scrub-shrub Wetland (freshwater wetland with majority scrub-shrub cover)
15      Palustrine Emergent Wetland  (freshwater wetland with majority herbaceous cover)
17      Estuarine Scrub-shrub Wetland  (estuarine wetland - salinity > 0.5% - with majority scrub-shrub cover)
18      Estuarine Emergent Wetland (estuarine wetland - salinity > 0.5% - with majority herbaceous cover)
19      Unconsolidated Shore (rocky shore, mudflats, sand beach, exposed lake shoreline)
20      Bare Ground  (open quarries and pits, granite outcrops and peaks)
21      Open Water   (water bodies typically > 30m wide)
22      Palustrine Aquatic Bed (freshwater algal mats, floating mats)
23      Estuarine Aquatic Bed (estuarine - salinity > 0.5% mats - seaweed, kelp, eelgrass beds)

NLCD 2001 landcover for 1995
Using the same exact methodology, but based on circa-1995 imagery, a second landcover map is produced for the purposes of change detection.  It has the same properties as the 2001 landcover data.  For details, see the the metadata.

image showing example of forested area in NLCD 1995 data  image showing example of forested NLCD 2001 data
Samples of 1995 (left) and 2001 (right) NLCD 2001 landcover data.  Black arrows indicate areas where shrublands have regrown to mixed or deciduous forest in that time period.  The location is in Kenduskeag and Glenburn in the Kenduskeag Stream watershed.

NLCD 2001 change 1995-2001
This layer depicts landcover changes that occured between the 1995 and 2001 datasets.  There are 147 classes in this layer based on the number of change combinations occurring in zone 66.  For details, see the metadata.  Note to users:  those of you with DVD data will see additional classes which are unchanged (i.e. evergreen forest to evergreen forest).  These have been removed in the data available for DEP, state users, and anybody downloading the data from MEGIS, since they actually indicate no change.  DVD data pixel values for this layer correspond to the NLCD_VALUE field in the classes list linked above.

image showing example of landcover change
The same area showin in the change data.  Light blue indicates a change from scrub-shrub to mixed forest, magenta is scrub-shrub to deciduous forest.

NLCD 2001 imperviousness
This layer depicts the % imperviousness in each 30m pixels based on the 2001 LandSat data.  This layer also has greater thematic accuracy than its MELCD 2004 counterpart (which has just a simple yes/no classification), but much lower spatial resolution (30m vs. 5m in MELCD 2004).  Accuracy is estimated at 88%.  For details, see the metadata.  This layer was used to derive the developed classes in the NLCD 2001 landcover layers.

NLCD 2001 canopy closure
Another layer used to derive the NLCD 2001 landcover data is this one which depicts % canopy closure of trees in each 30m pixel.  Accuracy is estimated at 93% based on cross-validation.  For details, see the metadata.

example of NLCD imperviousness   example of NLCD canopy data
(LEFT) NLCD 2001 imperviousness data in Bangor, darker pixels are more impervious, with black = 100% and white = 0%.  This is in Bangor where Kenduskeag stream enters the Penobscot River.  (RIGHT) NLCD 2001 canopy data in the same Kenduskeag/Glenburn location as above.  Darker green means more canopy with darkest green = 100% and white = 0%.
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