  We model the gas dynamics of barred galaxies using a three-dimensional,
high-resolution, $N$-body+hydrodynamical simulation and apply it to the Milky
Way in an attempt to reproduce both the large-scale structure and the clumpy
morphology observed in Galactic H\emissiontype{I} and CO $l-v$ diagrams. Owing
to including the multi-phase interstellar medium, self-gravity, star-formation
and supernovae feedback, the clumpy morphology, as well as the large-scale
features, in observed $l-v$ diagrams are naturally reproduced. We identify in
our $l-v$ diagrams with a number of not only large-scale peculiar features such
as the '3-kpc arm', '135-km s$^{-1}$ arm' and 'Connecting arm' but also clumpy
features such as `Bania clumps', and then link these features in a face-on view
of our model. We give suggestions on the real structure of the Milky Way and on
the fate of gas clumps in the central region.
