  We report an analysis of the accessibility between different locations in big
cities, which is illustrated with respect to London and Paris. The effects of
the respective underground systems in facilitating more uniform access to
diverse places are also quantified and investigated. It is shown that London
and Paris have markedly different patterns of accessibility, as a consequence
of the number of bridges and large parks of London, and that in both cases the
respective underground systems imply in general increase of accessibility.
