  The Fermi-LAT data accumulated over 7 years of {\gamma}-ray observations,
together with the high resolution gas (CO & HI) and the dust opacity maps, are
used to study the emissivity of {\gamma}-rays induced by interactions of cosmic
rays (CRs) with the interstellar medium. Based on the dust opacity templates,
the {\gamma}-ray emissivity was measured for 36 segments of the Galactic plane.
Furthermore, the {\gamma}-ray emissivity was evaluated in six Galactocentric
rings. Both the absolute emissivity and the energy spectra of {\gamma}-rays
derived in the interval 0.2-100 GeV show significant variations along the
galactic plane. The density of CRs, derived under the assumption that
{\gamma}-rays are predominately produced in CR interactions with the
interstellar gas, is characterised by a strong radial dependence. In the inner
Galaxy the CR density substantially exceeds the density in the outer parts of
the Galaxy: by a factor of a few at 10 GeV, and by more than an order of
magnitude at 1 TeV. Remarkably, the energy distribution of CRs appears to be
substantially harder than the energy spectrum obtained from direct measurements
of local CRs. At the same time, the flux and the energy spectrum of multi-GeV
protons derived from {\gamma}-ray data in the outskirts of the Galaxy is quite
close to the measurements of local CRs.
