  We explore geometry of London's streets using computational mode of an
excitable chemical system, Belousov-Zhabotinsky (BZ) medium. We virtually fill
in the streets with a BZ medium and study propagation of excitation waves for a
range of excitability parameters, gradual transition from excitable to
sub-excitable to non-excitable. We demonstrate a pruning strategy adopted by
the medium with decreasing excitability when wider and ballistically
appropriate streets are selected. We explain mechanics of streets selection and
pruning. The results of the paper will be used in future studies of studying
dynamics of cities with living excitable substrates.
