  In this talk we will discuss the physics reach of the atmospheric neutrino
data collected by a future megaton-class neutrino detector. First we will
discuss the potentialities of atmospheric neutrinos on general basis,
presenting our results in the form of neutrino oscillograms of the Earth:
contour plots in the neutrino energy--nadir angle plane. In this context we
will analyze in detail the various signatures related to theta_13, to the
neutrino mass hierarchy, to the octant of theta_23 and to the delta_CP phase
which appear for different values of the neutrino energy and baseline. Then we
will consider concrete experimental setups, showing that synergic effects exist
between atmospheric and long-baseline neutrino data: the combination of the two
data sets is much more powerful than the simple sum of the sensitivity of each
individual data sample.
