"This atlas is a product of the Montana Gap Analysis project (MT-GAP). It is intended to serve as a reference to accompany and supplement the project’s digital data in a geographic information system (GIS). We begin with a description of the land cover classification system that we used, followed by a brief overview of the mapping process. Then, for each cover type, we provide a statewide map of its distribution, a photograph, a descriptive summary of its size and spatial characteristics, and plant composition.

Much of the information contained in the atlas was obtained from a digital GIS database which is also available (see “How to obtain GAP data” below). Users are reminded that the digital source data were derived and assembled for the purpose of mapping land cover at relatively broad scales. Although the smallest mapping unit was 90 m2 pixels, such small units are not visible on the atlas maps, nor should one assume that the digital data warrant use at such fine scale. Thematic map accuracy was calculated using fuzzy sets and a bootstrap procedure which allowed misclassification probabilities to be estimated at the location of each training data point. Absolute thematic accuracy for 45 cover types averaged 61.4%, ranging from 4.4% for Western Hemlock to 93.2% for Missouri Breaks; at the “acceptable” level, mean accuracy increased to nearly 89%."

from: Montana GAP Analysis, Montana Land Cover Atlas, by Foster B. Fisher, Chris Winne, Michele M. Thornton, Troy P. Tady, Zhenkui Ma, Melissa M. Hart, and Roland L. Redmond. September 30, 1998.