  Core collapse supernovae of massive (> 8 Mo) stars are formed primarily in OB
associations and help blow giant superbubbles, where their collective shocks
accelerate most of the Galactic cosmic rays. The spatial distribution of these
stars is thus important to our understanding of the propagation of the observed
cosmic rays. In order to better model the Galactic cosmic-ray distribution and
propagation, we construct s three-dimensional spatial model of the massive star
distribution based primarily on the emission of the H II envelopes surrounding
the giant superbubbles which are maintaned by the ionizing radiation of the
embedded O stars. The Galactic longitudinal distribution of the 205 micron N II
rsdistion emitted by these H II envelopes is used to infer the spatial
distribution of the superbubbles. We find that the Galactic superbubble
distribution is dominated by the contribution of massive star clusters residing
in the spiral arms.
