Much of the recent confidence in the future of science and technology stems from advances in scientific visualisation. But is it right to assume that visual - and especially pictorial - measures carry special epistemic weight in the context of scientific reasoning? Do pictorial approaches have any surpluses, compared to other semiotic types? This book delves into these issues from the point of view of the philosophy of science. New examples from the field of scientific visualisation are introduced in order to account for the epistemic weight and surpluses of syntactically dense - pictorial - symbol systems.