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. Mapping zone 21 encompasses whole or portions of several states, including the states of Idaho, Montana, and Wyoming. Questions about the NLCD mapping zone 21 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.
Conceptually, the descriptive tree is a classification tree generated by using the final minimum-map- unit land cover product (1 acre) as training data, and Landsat and other ancillary data as predictors. The goal of the descriptive tree is to summarize the effects of boosted trees (10 sequential classification trees) into a single condensed decision tree that can be used as a diagnostic tool for the classification process. This descriptive tree can be used to assess the relative importance of each of the input data sets on each land cover class. Such information may also be useful to customize the minimum-mapping-unit classification to meet a user's specific needs through raster modeling. Descriptive trees usually capture 60 to 80% of the information from the original land cover data.
The leaf or terminal nodes of the descriptive tree are assigned to sequential numbers (called node numbers) and mapped across the entire mapping zone on a pixel-by-pixel basis. These node numbers can then be matched with the various conditional statements associated with each respective terminal node. This spatial layer appears similar to a cluster map, but is the result of a supervised classification - not an unsupervised clustering. This node map can potentially be used as input by users to customize NLCD land cover, by linking the spatial extent of an individual node with the rules of the conditional statement.
The Land Cover spatial classification confidence data layer is provided to users to help determine the per-pixel spatial confidence of the NLCD 2001 land cover prediction from the descriptive tree. The C5 algorithm produces an estimate (a value between 0% and 100%) that indicates the confidence of rule predictions at each node based on the training data. This spatial confidence map should be considered as only one indicator of relative reliability of the land cover classification, rather than a precise estimate. Users should be aware that this estimate is made based on only training data, and is derived from a generalized descriptive decision tree that reproduces the final land cover data. However, this layer provides valuable insight for a user to determine the risk or confidence they choose to place in each pixel of land cover.
A logic statement from a descriptive tree classification describes each classification rule for each classified pixel. An example of the logic statement follows:
IF tasseled-cap wetness > 140 and imperviousness = 0 and canopy density < 4, then classify as Water
This logic file can be used in combination with the spatial node map to identify classification logic and allow modifications of the classification based on user's knowledge and/or additional data sets.
Additional information may be found at <http://www.mrlc.gov/mrlc2k_nlcd.asp>.
To conduct the land cover classification using DT, a large quantity of training data is required. For mapping zone 21, training data were collected from several combined sources including Northwest Region Bureau of Indian Affairs, USFS R1 Landbird Monitoring Program (Permanent Plots), Student Conservation Association, and Earth Satellite Corporation.
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 combination model approach using multiple datasets (zone 21 impervious data, single-date Landsat reflectance imagery, and GoogleEarth). The models used to derive the urban and sub-urban areas layered portions of each dataset to achieve the final output.
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.
Acquisition dates of Landsat ETM+ (TM) scenes used for land cover classification in zone 21 are as follows:
SPRING-
Index 1 for Path 37/Row 29 on 05/24/01 = Scene_ID 7037029000114450
Index 2 for Path 37/Row 29 on 06/01/01 = Scene_ID 5037029000115210
Index 2 for Path 37/Row 30 on 06/01/01 = Scene_ID 5037030000115210
Index 1 for Path 37/Row 30 on 05/24/01 = Scene_ID 7037030000114450
Index 3 for Path 38/Row 28 on 05/23/01 = Scene_ID 5038028000114310
Index 3 for Path 38/Row 29 on 05/23/01 = Scene_ID 5038029000114310
Index 3 for Path 38/Row 30 on 05/23/01 = Scene_ID 5038030000114310
Index 3 for Path 38/Row 31 on 05/23/01 = Scene_ID 5038031000114310
Index 4 for Path 39/Row 28 on 06/26/02 = Scene_ID 7039028000217750
Index 5 for Path 39/Row 29 on 06/04/00 = Scene_ID 7039029000015650
LEAF ON (Summer)-
Index 1 for Path 37/Row 29 on 07/30/02 = Scene_ID 7037029000221150
Index 2 for Path 37/Row 30 on 07/27/01 = Scene_ID 7037030000120850
Index 3 for Path 37/Row 30 on 07/09/03 = Scene_ID 5037030000319010
Index 4 for Path 38/Row 28 on 07/05/02 = Scene_ID 7038028000218650
Index 4 for Path 38/Row 29 on 07/05/02 = Scene_ID 7038029000218650
Index 5 for Path 38/Row 30 on 08/01/03 = Scene_ID 5038030000321310
Index 6 for Path 38/Row 31 on 06/29/00 = Scene_ID 7038031000018150
Index 7 for Path 39/Row 28 on 07/12/02 = Scene_ID 7039028000219350
Index 7 for Path 39/Row 29 on 07/12/02 = Scene_ID 7039029000219350
Index 8 for Path 39/Row 29 on 07/01/01 = Scene_ID 5039029000118210
Index 7 for Path 39/Row 30 on 07/12/01 = Scene_ID 7039030000119350
LEAF-OFF (Fall)-
Index 1 for Path 37/Row 29 on 09/08/99 = Scene_ID 7037029009925150
Index 1 for Path 37/Row 30 on 09/08/99 = Scene_ID 7037030009925150
Index 2 for Path 37/Row 31 on 09/10/00 = Scene_ID 7037031000025450
Index 3 for Path 38/Row 28 on 09/15/99 = Scene_ID 7038028009925850
Index 4 for Path 38/Row 28 on 09/02/03 = Scene_ID 5038028000324510
Index 3 for Path 38/Row 29 on 09/15/99 = Scene_ID 7038029009925850
Index 5 for Path 38/Row 29 on 09/20/01 = Scene_ID 7038029000126350
Index 3 for Path 38/Row 30 on 09/15/99 = Scene_ID 7038030009925850
Index 6 for Path 38/Row 31 on 10/03/00 = Scene_ID 7038031000027750
Index 7 for Path 39/Row 28 on 09/22/99 = Scene_ID 7039028009926550
Index 7 for Path 39/Row 29 on 09/22/99 = Scene_ID 7039029009926550
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.