One hundred years after their discovery by the Austrian physicist Victor Hess, the origin of cosmic rays is still unclear. The detection of TeV gamma rays from supernova remnants (SNRs) by the experiment HESS has strengthened the hypothesis that primary Galactic cosmic-ray electrons are accelerated in SNRs up to the knee energy, where the power-law cosmic ray spectrum changes. Despite this extraordinary recent discovery the question of the origin of cosmic rays is still open, and even if the SNRs prove to be sources of cosmic ray electrons, no compelling evidence for the acceleration of hadrons in SNRs has until now been found. The diffuse gamma radiation arising from the interaction of cosmic-ray particles with matter and radiation in the Galaxy is one of the few probes available to study the origin of cosmic rays. Nevertheless the predictions of the gamma ray flux based upon the measured Galactic matter density and the cosmic-ray spectrum and intensity measured at Earth are in disagreement with the measurements obtained by the EGRET and Milagro detectors. The proposed project aims to investigate the features of the gamma ray spectrum from each direction of the Galaxy and to compare the gamma ray data with the ISM data and use the results as a probe of the cosmic ray flux in the different regions of the galaxy. The regions where the galactic gamma ray flux cannot be explained by interactions of a cosmic ray flux similar to that measured close to the Sun with the passive ISM targets, will be interesting probes of the sites of CR injection.