Pixels (or grid cells) in each map are assigned to one of the discrete categories used to describe that data theme. Categories for a vegetation data theme, for example, are listed in Table 2. After overlaying the maps to form a composite map, the categories from each data layer in the composite map are represented as a string of characters called a landscape condition label [4]. Each character of this label reflects a category from one of the original maps. For example, the composite map label 2413 might designate a grid cell belonging (moving from right to left) to the third vegetation-cover category, the first aspect category, the fourth land-ownership class, and second range of elevation.
Table 2: Sample category values for vegetation in LUCAS .