  High-energy gamma rays of interstellar origin are produced by the interaction
of cosmic-ray (CR) particles with the diffuse gas and radiation fields in the
Galaxy. The main features of this emission are well understood and are
reproduced by existing CR propagation models employing 2D Galactocentric
cylindrically symmetrical geometry. However, the high-quality data from
instruments like the Fermi Large Area Telescope reveal significant deviations
from the model predictions on few to tens of degree scales indicating the need
to include the details of the Galactic spiral structure and thus require 3D
spatial modelling. In this paper the high-energy interstellar emissions from
the Galaxy are calculated using the new release of the GALPROP code employing
3D spatial models for the CR source and interstellar radiation field (ISRF)
densities. Three models for the spatial distribution of CR sources are used
that are differentiated by their relative proportion of input luminosity
attributed to the smooth disc or spiral arms. Two ISRF models are developed
based on stellar and dust spatial density distributions taken from the
literature that reproduce local near- to far-infrared observations. The
interstellar emission models that include arms and bulges for the CR source and
ISRF densities provide plausible physical interpretations for features found in
the residual maps from high-energy gamma-ray data analysis. The 3D models for
CR and ISRF densities provide a more realistic basis that can be used for the
interpretation of the non-thermal interstellar emissions from the Galaxy.
