(By Leon Stassen): "This map shows the areal distribution of zero copula encoding for predicate nominals. That is, the map indicates whether a given language is like English, in which predicate nominals always require an overt copula..., or rather like Russian, in which omission of the copula is allowed for at least some constructions..."
The Grammaticon's "copula" is a form, i.e. it is not "zero" by definition. Stassen's "zero copula" would be treated as absence of a copula. The notion of "predicate nominal" does not exist in Grammaticon, though the predicate of classificational clauses (a subtype of duonominal clauses) could be called "nominal predicate".