  We develop an approach to characterize excited states of disordered many-body
systems using spatially resolved structures of entanglement. We show that the
behavior of the mutual information (MI) between two parties of a many-body
system can signal a qualitative difference between thermal and localized phases
-- MI is finite in insulators while it approaches zero in the thermodynamic
limit in the ergodic phase. Related quantities, such as the recently introduced
Codification Volume (CV), are shown to be suitable to quantify the correlation
length of the system. These ideas are illustrated using prototypical
non-interacting wavefunctions of localized and extended particles and then
applied to characterize states of strongly excited interacting spin chains. We
especially focus on evolution of spatial structure of quantum information
between high temperature diffusive and many-body localized phases believed to
exist in these models. We study MI as a function of disorder strength both
averaged over the eigenstates and in time-evolved product states drawn from
continuously deformed family of initial states realizable experimentally. As
expected, spectral and time-evolved averages coincide inside the ergodic phase
and differ significantly outside. We also highlight dispersion among the
initial states \emph{within} the localized phase -- some of these show
considerable generation and delocalization of quantum information.
