Emerald City was a city mentioned in Earth literature.
Commander Trip Tucker compared the capital city of Coridan to Emerald City in 2151. (ENT: "Shadows of P'Jem")
Emerald City, according to the Star Trek Encyclopedia, 4th ed., vol. 1, p. 234, was a location mentioned by the author L. Frank Baum in his book The Wizard of Oz and in subsequent film adaptations of the work. Described by the authors of this reference work as "gloriously beautiful", Emerald City was the capital of the Land of Oz.