CO observations,geometry, and galactic structure

2.6 mm carbon monoxide and 21 cm hydrogen line observations of the Galaxy define six directions where gas is seen tangentially along a spiral feature and four directions where extended structures cross theR=R ₀ circle. These directions provide a geometrical framework for any spiral structure pattern. Also simple equations are derived to define the normalized radiusR/R ₀ of gas with a particular radial velocity in terms of the observed tangential velocity of gas with the sameR/R ₀=sinl _T, without specific knowledge of (R), ₀ orR ₀.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.