  We present a novel method to model galactic scale star formation and the
resulting emission from star clusters and the multi-phase interstellar medium.
We combine global parameters, such as SFR and CMF, with {\sc warpfield} which
provides a description of the feedback-driven evolution of individual
star-forming regions. Our approach includes stellar evolution, stellar winds,
radiation pressure, supernovae, all of which couple to the dynamical evolution
of the parental cloud in a highly non-linear fashion. The heating of diffuse
gas and dust is calculated self-consistently with the age, mass and density
dependent escape fractions of the local star-forming regions. From this we
construct the interstellar radiation field at any point in the galaxy, and we
employ the multi-frequency Monte Carlo radiative transfer code {\sc polaris} to
produce synthetic emission maps for the one-to-one comparison with
observational data.
  We demonstrate the capabilities of our approach by applying the method to a
Milky Way like galaxy built-up in a high-resolution cosmological MHD
simulation. We give three examples. First, we compute the multi-scale
distribution of electron $n_{e^-}$ and $T_{e^{-}}$ and synthesize the MW
all-sky H$\alpha$ emission. We use a multipole expansion method to show that
the resulting maps are consistent with observations. Second, we predict the
expected \SIII 9530~\AA\ emission. This line is a key target of several planned
large survey programs. It suffers less extinction than other diagnostic lines
and provides information about star formation in very dense environments that
are otherwise observationally not readily accessible. Third, we explore the
effects of differential extinction as seen by an extra-galactic observer, and
discuss the consequences for the correct interpretation of \Ha emission as a
star-formation rate tracer at different viewing angles.(abridged)
