The categories of class, subclass, group, and formation are physiognomic and therefore applicable to Gap Analysis. These terms refer to concepts of potential or climax vegetation rather than actual or existing vegetation, and their use as applied to actual vegetation has been the source of some confusion. Because Gap Analysis is concerned with present-day conditions, all terms and concepts used herein refer to actual vegetation, whether in seral or climax stages of development. All references and applications are made to actual land cover rather than historic land cover or potential climax vegetation. In order to create useful categories across both biotic and geographic scales, it is necessary to use both subdivisions and aggregations.
Subdivision begins with a whole and divides it into smaller units according to similarities.
Aggregation begins with a set of individual objects and groups them according to similarities. The classification scheme is open-ended. The classification scheme is intended to be the super-structure upon which information can continuously be placed for meaningful analysis and interpretation. If greater resolution is desired for certain objects of interest the MMU may be smaller, for example, an MMU of 40 hectares is often used to resolve riparian areas. J. A variety of attributes may be attached to a given label or polygon that are not displayed in map format for Gap Analysis purposes.