  We have obtained new estimates of the Sun's distance from the symmetry plane
Zo and the vertical disk scale height h using currently available data on
stellar OB associations, Wolf-Rayet stars, HII regions, and Cepheids. Based on
individual determinations, we have calculated the mean Zo=-16+/-2 pc. Based on
the model of a self-gravitating isothermal disk for the density distribution,
we have found the following vertical disk scale heights: h = 40.2+/-2.1 pc from
OB associations, h = 47.8+/-3.9 pc from Wolf-Rayet stars, h=48.4+/-2.5 pc from
HII regions, and h = 66.2+/-1.6 pc from Cepheids. We have estimated the
surface, \sum=6 kpc^{-2}, and volume, D(Zo) = 50.6 kpc^{-3}, densities from a
sample of OB associations. We have found that there could be approximately 5000
OB associations in the Galaxy.
