Language uses location description with respect to spatial frames of reference.
These parameters characterize a reference frame. The paper describes the methods used in the English language and proposes exact definitions of egocentric, intrinsic or retinal relative reference frames, and egocentric or allocentric cardinal relative reference frames. Invariants of descriptions with respect to classes of reference frames are discussed and some hints for the pragmatic preference of one or the other reference frame suggested. Precise hypotheses can be formulated in the formalized framework to construct human subject tests to differentiate between these alternatives.