  We explore the longitude-velocity distribution of 6.7-GHz methanol masers in
the context of the inner structure of our Galaxy. We analyse the correlation in
velocities within this distribution and identify density enhancements
indicating large-scale regions of enhanced star formation. These are
interpreted as the starting points of the spiral arms and the interaction of
the Galactic bar with the 3-kpc arms. The methanol masers support the presence
of a long thin bar with a 45 degree orientation. Signatures of the full 3-kpc
arm structure are seen, including a prominent tangent at approximately -22
degrees Galactic longitude. We compare this distribution with existing models
of the gas dynamics of our Galaxy. The 3-kpc arm structure appears likely to
correspond to the radius of corotation resonance of the bar, with the bar on
its inner surface and the starting points of the spiral arms on its outer
surface.
