This is called in the schools proportio habitudinis (St Thomas's phrase here), sed non existentiae. I have written elsewhere: "There is an analog between the paper plan of the building and the building as it exists. . . . It is obvious that plan and building do not receive the same name in the same sense: yet there is some connexion and relation between the two, a relation of the less to the incomparably greater which it somehow exhibits and represents" (Oxford and Cambridge Conferences, second series, pp. 132, 133). Another, and possibly a more apt illustration, might be supplied by modern 'graphs,' I mean one of those 'curves of temperature,' or the like, which correspond to, but do not (except a very indirect or highly generic fashion) resemble the facts which they truly represent.
Of God and His Creatures: 3.54