A Morphological Classification of 18190 Molecular Clouds Identified in
  $^{12}$CO Data from the MWISP Survey
  We attempt to visually classify the morphologies of 18190 molecular clouds,
which are identified in the $^{12}$CO(1-0) spectral line data over $\sim$ 450
deg$^{2}$ of the second Galactic quadrant from the Milky Way Imaging Scroll
Painting project (MWISP). Using the velocity-integrated intensity maps of the
$^{12}$CO(1-0) emission, molecular clouds are first divided into unresolved and
resolved ones. The resolved clouds are further classified as non-filaments or
filaments. Among the 18190 molecular clouds, $\sim$ 25 $\%$ are unresolved,
$\sim$ 64$\%$ are non-filaments, and $\sim$ 11$\%$ are filaments. In the terms
of the integrated flux of $^{12}$CO(1-0) spectra of the whole 18190 molecular
clouds, $\sim$ 90$\%$ are from filaments, $\sim$ 9$\%$ are from non-filaments,
and the rest $\sim$ 1$\%$ are from unresolved sources. Although non-filaments
are dominant in the number of the discrete molecular clouds, filaments are the
main contributor of $^{12}$CO emission flux. We also present the number
distributions of physical parameters of the molecular clouds in our catalog,
including their angular sizes, velocity spans, peak intensities of
$^{12}$CO(1-0) emission, and $^{12}$CO(1-0) total fluxes. We find that there is
a systematic difference between the angular sizes of the non-filaments and
filaments, with the filaments tending to have larger angular scales. The
H$_{2}$ column densities of them are not significantly different. We also
discuss the observational effects, such as those induced by the finite spatial
resolution, beam dilution and line-of-sight projection, on the morphological
classification of molecular clouds in our sample.
