  We derived the three-dimensional distribution of HI gas in the Milky Way
Galaxy using the latest HI survey data cubes and rotation curves. The distance
of the HI gas was determined by the kinematic distance using a rotation curve.
We solved the near-far problem in the inner Galaxy by a fitting method which
involves introducing a model of vertical HI distribution.
  In our resultant maps we could trace three prominent arms: the
Sagittarius-Carina arm, the Perseus arm, and the Outer arm. These three arms
were found to be logarithmic spiral arms. The pitch angles of the
Sagittarius-Carina, Perseus, and Outer arms were estimated to be about
$11\arcdeg$, $18\arcdeg$, and $7\arcdeg$, respectively. The Sun is located in a
region rich in HI gas between the Sagittarius-Carina arm and the Perseus arm.
  The HI disk shows large and asymmetric warping in the outer disk: the HI disk
goes up to about 1.5 kpc above the Galactic plane in the northern hemisphere,
and down to about 1 kpc in the southern hemisphere, which means asymmetric
warping. The inner HI disk is also found to be tilting. The radius of the HI
disk is about 17 kpc and the HI mass within this radius is estimated to be $2.5
\times 10^9$ M$_\odot$, which corresponds to 1.5 % of the dynamical mass
predicted from the rotation curve. We also found that the HI outskirt is
largely swelling in the fourth quadrant, and hence the Galaxy is significantly
lopsided. The scale-height of the HI layer increases with the radius, and is
correlated with the HI volume density at the centroid of the HI layer.
