Scalar Clusters are used to construct Thesaurus. There can be a Global Thesaurus (GT) or a Local Thesaurus (GT). GT is constructed using all terms in all documents in the corpus whereas LT construction is query specific and is constructed by only using terms in the query.
LT is better than GT in scenarios when a term has a significant meaning wrt the query. For e.g. if we are looking for operation wrt computer science documents and construct a GT, we might get many uses of term 'operating' which will dilute the significance of the term.
