Determination of the GHC is based upon a sequence of five dichotomous divisions related to a set of six super-categories, (Urban, Cultivated, Sparsely Vegetated, Tree and Shrubs, Herbaceous wetland and other Herbaceous) which determine the series of Non Life Form Categories (NLF) and Life Form Categories (LF) that can be used to identify the appropriate GHC.
The GHC is determined first so that a decision is made in the field to ascribe the given element a single category. See also General Habitat Categories.For determining the GHCs there are only two percentage rules:
1) over 70% for single GHCs
2) 40-60% for GHCs that are combinations of two habitats.
Elements with 40-60% cover of two Life Forms or two non Life Form categories belonging to the same super category or in case of TRS belonging to the same height category, are also GHCs, but with a double code, e.g. ROC/GVR or SHY/EHY or with a triple code if belonging to the TRS supercategory e.g. mixed Deciduous/Conifer Forest (FPH/DEC/CON). If there are equal proportions of life forms then precedence rules are provided. The precedence will be given in the order of the GHCs as listed.