extrapolate

To infer by extending known information.

With fresh material, taxonomic conclusions are leavened by recognition that the material examined reflects the site it occupied; a herbarium packet gives one only a small fraction of the data desirable for sound conclusions. Herbarium material does not, indeed, allow one to extrapolate safely: what you see is what you get[…]

To estimate the value of a variable outside a known range from values within that range by assuming that the estimated value follows logically from the known ones