The components from which the gamma-ray luminosity of the Galaxy is known to arise are grouped into three classes. A relative contribution greater than about 34% belongs to the strong, discrete sources defined by the acceptance criteria of the 2CG catalogue. Although these are mostly unidentified, the population-type information derivable from evolution constraints and the observed galactocentric radius justifies this estimate. A class contribution of about 20% is derived from radio data for the case of normal radio pulsars, and the remainder of the gamma-ray luminosity is attributed to cosmic ray interactions with the diffuse matter. No evidence is found for a positive correlation of cosmic ray and gas densities. Instead, the large gamma-ray luminosity contributed by a Population I component explains the gamma-ray background longitude profile for which the correlation hypothesis was advanced.