Predicative noun and predicative locative phrases tend to be encoded differently in the past, with a form of was favoured in predicative noun phrases and been favoured in predicative locative phrases. The distinction also appears to be related, however, to the phenomenon of grounding in discourse and the boundedness and/or stativity of verb situations; cf. Hackert (2004: 114). In present contexts, the form of the verb employed is usually is (thus, nominal and locational predication may be encoded in the same way there); however, as in African American English, the copula tends to be absent much more frequently before a locational expression than before a nominal one; cf. e.g. Shilling (1978: 29, 31). Finally, alternative forms (cf. Feature 75 "Predicative locative phrases") such as de are restricted to locative contexts.
Source: Shilling 1978: 49
Source: Shilling 1978: 60
Source: Shilling 1978: 87
Source: Shilling 1978: 72