A set of parameters to characterize azimuthal profiles of galaxies is proposed and applied to the spiral structure of the galaxies NGC 1832 and NGC 7479 observed in the B and I passbands. Interpretations of the observations in terms of the two most widely discussed theories of star formation, the spiral density wave theory and that of self-stochastic propagation of star formation, are considered. NGC 7479, with well defined arms, seems to maintain a leading density wave; evidence is presented for a phase separation in the B and I bands corresponding to star formation stimulated by the passage of the wave. NGC 1832, with more flocculent spiral arms, presents a more confused interpretational pattern.