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associated with the dense peaks of infrared dark clouds have now been  surveyed for \ammonia \ emission \citep{Purcell2012b}, yielding high-spectral resolution  velocity measurements towards gas whose density typically exceeds  $10^4$ \cc. cm$^{-3}$.  In follow-up spectral-line surveys to the ATLASGAL dust-based survey of the Galactic Plane \citep{Beuther2012a}, \citet{Wienen2012} have  measured \ammonia \ emission in nearly 1000 locations. The ThrUMMs Survey aims to map the entire fourth quadrant of the Milky Way in CO and higher-density tracers \citep{BarnesPeter2010}, which also holds the  potential for more high-resolution velocity measurements.