  We describe the development of the model for interstellar gamma-ray emission
that is the standard adopted by the LAT team and is publicly available. The
model is based on a linear combination of templates for interstellar gas column
density and for the inverse Compton emission. The spectral energy distributions
of the gamma-ray emission associated with each template are determined from a
fit to 4 years of Fermi-LAT data in 14 independent energy bins from 50 MeV to
50 GeV. We fit those distributions with a realistic model for the emission
processes to extrapolate to higher energies. We also include large-scale
structures like Loop I and the Fermi bubbles following an iterative procedure
that re-injects filtered LAT counts residual maps into the model. We confirm
that the cosmic-ray proton density varies with the distance from the Galactic
center and find a continuous softening of the proton spectrum with this
distance. We observe that the Fermi bubbles have a shape similar to a catenary
at their bases.
