  We present the azimuthally averaged radial distribution of 748 regions of OB
star formation in the whole galactic disk, based on our previous CS(2-1) survey
of UC H II regions. Embedded massive stars produce a total FIR luminosity of
1.39E8 Lsun within the range 0.2<R/Ro<2 in galactocentric radius. We find 492
massive star forming regions within the solar circle, producing 81% of the
total FIR luminosity. Separate analyses of the 349 sources in the I and II
quadrant (north), and of the 399 sources in the III and IV quadrant (south),
yield FIR luminosities (extrapolated to the complete galactic disk) of 1.17E8
Lsun and of 1.60E8 Lsun, respectively. Massive star formation is distributed in
a layer with its centroid Zo(R) following that of molecular gas for all
galactocentric radii, both north and south. Its thickness for R<Ro is ~73 pc
(FWHM), 62% the thickness of the molecular gas disk. The FIR luminosity
produced by massive stars has a well defined maximum at R=0.55Ro, with a
gaussian FWHM of 0.28Ro - compared with 0.51Ro for the H2 surface density
distribution. Toward the outer Galaxy, down from the maximum, the face-on FIR
surface luminosity decays exponentially with a scale length of 0.21Ro, compared
with 0.34Ro for the H2 surface density. Massive star formation per unit H2 mass
is maximum for R~0.55Ro in the southern Galaxy, with a FIR surface luminosity
to H2 surface density ratio of 0.41Lsun/Msun, compared with 0.21Lsun/Msun at
the same radius in the north, and with an average of ~0.18Lsun/Msun for the
whole galactic disk within the solar circle.
