Impact of distance determinations on Galactic structure. I. Young and
  intermediate-age tracers
  Here we discuss impacts of distance determinations on the Galactic disk
traced by relatively young objects. The Galactic disk, about 40 kpc in
diameter, is a cross-road of studies on the methods of measuring distances,
interstellar extinction, evolution of galaxies, and other subjects of interest
in astronomy. A proper treatment of interstellar extinction is, for example,
crucial for estimating distances to stars in the disk outside the small range
of the solar neighborhood. We'll review the current status of relevant studies
and discuss some new approaches to the extinction law. When the extinction law
is reasonably constrained, distance indicators found in today and future
surveys are telling us stellar distribution and more throughout the Galactic
disk. Among several useful distance indicators, the focus of this review is
Cepheids and open clusters (especially contact binaries in clusters). These
tracers are particularly useful for addressing the metallicity gradient of the
Galactic disk, an important feature for which comparison between observations
and theoretical models can reveal the evolutionary of the disk.
