ABSTRACT
A second salient feature of statistical graphs is their providing a ‘spatial analogue’ of quantitative values. That is, quantities are expressed in spatial magnitudes. In fact, one of the first comprehensive theories of graph reading and comprehension, Cleveland’s basic task model (Cleveland and McGill, 1984), consists of an ordering of types of analogical coding (which they called ‘specifiers’), such as length, angle and area, in terms of their relative effectiveness for reading off and comparing numeric values.
