A guided map to the Spiral arms in the galactic disk of the Milky Way
  An up-to-date overview of the recent history is given, aiming to present a
helpful working guide to the literature and at the same time introduce key
systems and observational results, starting from the Sun and going towards the
Galactic Center and parts of the Zona Galactica Incognita, and beyond.
  We start by presenting an observational view of the Milky Way's disk plane
(cartographic. dynamical, chemical cross-cut, magnetic). This included the four
long spiral arms in the disk of the Milky Way (fig.1), their geometry (fig.2),
component, velocity (fig.3), their widths and internal layers as well as
onion-like ordered offsets (fig.4), the central galactic bars, arm tangents,
arm pitch and arm shape, arm origins near the Galactic Center (fig.5), and
other possible players in the spiral arms, such as the magnetic field (fig.6)
and the dark matter content.
  After, we present a basic analysis of some theoretical predictions from
galactic arm formation: numerical simulations or analytical theories, and
observations are checked against predictions from various numerical simulations
and analytical (theoretical) models.
