Concerning the Distance to the Center of the Milky Way and its Structure
  The distance to the Galactic center inferred from OGLE RR Lyrae variables
observed in the direction of the bulge is Ro=8.1+-0.6 kpc. An accurate
determination of Ro is hindered by countless effects that include an ambiguous
extinction law, a bias for smaller values of Ro because of a preferential
sampling of variable stars toward the near side of the bulge owing to
extinction, and an uncertainty in characterizing how a mean distance to the
group of variable stars relates to Ro. A VI-based period-reddening relation for
RR Lyrae variables is derived to map extinction throughout the bulge. The
reddening inferred from RR Lyrae variables in the Galactic bulge, LMC, SMC, and
IC 1613 match that established from OGLE red clump giants and classical
Cepheids. RR Lyrae variables obey a period-colour (VI) relation that is
relatively insensitive to metallicity. Edge-on and face-on illustrations of the
Milky Way are constructed by mapping the bulge RR Lyrae variables in tandem
with cataloged red clump giants, globular clusters, planetary nebulae,
classical Cepheids, young open clusters, HII regions, and molecular clouds. The
sample of RR Lyrae variables do not trace a prominent Galactic bar or triaxial
bulge oriented at phi~25 degrees.
