The London Underground Diagram (LUD) is a cognitive
artifact and a well-known example of representational efficiency,
having been copied by urban transportation systems
worldwide. Here we describe the design of the LUD as an
example of cognitive niche construction happening through
iconic meaning of a problem space. We argue that the LUD's
meaning is grounded on the offer of opportunities for action
through diagrammaticity. Our examination suggest that
iconicity is at the core the cognitive niche construction.
