Viewed from within, the structure of our own Milky Way galaxy is harder  to appreciate. Interstellar dust also makes it difficult to measure  distances between stars in our galaxy with optical astronomy. Using  radio astronomy, we mapped the Milky Way in unprecedented detail. This  approach helps constrain its size and orientation, as well as the rate  of star formation within our galaxy. Xu Ye et al. mapped the nearest spiral arm of the Milky Way in unprecedented detail.

The abundant structures of the Local arm imply that the Milky Way may be not similar to the galaxy, M51, but the galaxy NGC 1232

See Sci. Adv. 10.1126.sciadv.1600878 (2016).  

http://science.sciencemag.org/content/sci/353/6307/1509.1.full.pdf?_ga=1.63094952.600763725.1447037578 

http://science.sciencemag.org/content/353/6307/twis.full