  In this work, we derive a spatially resolved map of the line-of-sight
velocity of the interstellar medium and use it, along with a second map of
line-of-sight velocity from Paper I of this series, to determine the nature of
gaseous spiral structure in the Milky Way. This map is derived from
measurements of the 1.527 $\mu$m diffuse interstellar band (DIB) in stellar
spectra from the APOGEE survey and covers the nearest 4-5 kpc of the Northern
Galactic plane. We cross-check this new DIB-based line-of-sight velocity map
with the map derived in Paper I and find that they agree. We then compare these
maps with line-of-sight velocity maps derived from simulations of
quasi-stationary density wave spiral structure and dynamic, or material, spiral
structure in a Milky Way-like galaxy. While none of the maps derived from these
simulations is an exact match to the measured velocity field of the Milky Way,
the measurements are more consistent with simulations of dynamic spiral
structure. In the dynamic spiral structure simulation that best matches the
measurements, the Perseus spiral arm is being disrupted.
