We report four trigonometric parallaxes for high-mass star-forming regions within 4 kpc of the Galactic center .
These measurements were made with the VLBA as part of the BeSSeL Survey .
By associating these sources kinematically with large-scale features in CO and H i longitude-velocity diagrams , we begin to outline some major features of the inner Milky Way : the Connecting arm , the near and far 3 kpc arms , and the Norma arm .
The Connecting arm in the first Galactic quadrant lies closer to the Galactic center than the far 3 kpc arm and is offset by the long-bar ’ s major axis near its leading edge , supporting the presence of an inner Lindblad resonance .
Assuming the 3 kpc arms are a continuous physical structure , the relative Galactocentric distance of its near and far sides suggests highly elliptical streamlines of gas around the bar ( s ) and a bar corotation radius , r _ { CR } \gtrsim 3.6 kpc .
At a Galactic longitude near 10 \arcdeg and a heliocentric distance of about 5 kpc , the near 3 kpc arm and the Norma arm intersect on a face-on view of our Galaxy , while passing at different Galactic latitudes .
We provide an accurate distance measurement to the W 31 star-forming complex of 4.95 ^ { +0.51 } _ { -0.43 } kpc from the Sun , which associates it with a bright CO feature belonging to the near 3 kpc arm .