  Young Stellar Objects (YSO) are newly formed stars from molecular clouds.
They stay close to where they were born and serve as good tracers to study gas
and star formation. During cloud evolution, young massive stars can disrupt the
surrounding gas through stellar feedback, changing the gas distribution. We
study the distribution of the gas around a sample of YSO associations located
at $d \lesssim 3.5 \;\rm kpc$ from the Sun by comparing the location and
morphology between $^{12}$CO (J = 1$-$0) emission, Planck 870 $\mu$m maps and
YSO associations. Based on the spatial distribution of the gas compared to that
of the YSOs, we classify the YSO associations into six types: direct, close,
bubble, complex, diffuse, and clean associations. The complex associations are
large structures consisting of both gas-rich and gas-poor segments. We study
the velocity dispersion-size relation toward different association types. From
the ratio between different types, we estimate a feedback time of $\approx$ 1.7
Myr in the solar neighborhood. The sample sets a solid foundation to explore
the relationship between interstellar medium evolution, star formation, and
Galaxy structure.
