This article explores the representational structures of numeration sy
stems and the cognitive factors of the representational effect in nume
rical tasks, focusing on external representations and their interactio
ns with internal representations. Numeration systems are analyzed at f
our levels: dimensionally, dimensional representations, bases, and sym
bol representations. The representational properties at these levels a
ffect the processes of numerical tasks in different ways and are respo
nsible for different aspects of the representational effect. This hier
archical structure is also a cognitive taxonomy that can classify near
ly all numeration systems that have been invented across the world. Mu
ltiplication is selected as an example to demonstrate that complex num
erical tasks require the interwoven processing of information distribu
ted across internal and external representations. Finally, a model of
distributed numerical cognition is proposed and an answer to the quest
ion of why Arabic numerals are so special is provided.