Sentence:  These differences in turn result from the fact that my Yokuts vocabularies were built up of terms selected mainly to insure unambiguity of English meaning between illiterate informants and myself , within a compact and uniform territorial area , but that Hoijer 's vocabulary <WSD>is</WSD> based on Swadesh 's second glottochronological list which aims at eliminating all items which might be culturally or geographically determined . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)