The dense galactic environments of the Milky Way
  Star formation takes place in the dense gas phase, and therefore a simple
dense gas and star formation rate relation has been proposed. With the advent
of multi-beam receivers, new observations show that the deviation from linear
relations is possible. In addition, different dense gas tracers might also
change significantly the measurement of dense gas mass and subsequently the
relation between star formation rate and dense gas mass. We report the
preliminary results the DEnse GAs in MAssive star-forming regions in the Milky
Way (DEGAMA) survey that observed the dense gas toward a suit of
well-characterized massive star forming regions in the Milky Way. Using the
resulting maps of HCO$^{+}$ 1--0, HCN 1--0, CS 2--1, we discuss the current
understanding of the dense gas phase where star formation takes place.
