Abstract: Since the systematic discovery of filamentary structures in molecular clouds by the Herschel observations, more and more attention has been paid to filaments. Molecular clouds usually exhibit filamentary structures, within which a significant fraction of gravitationally bound dense cores and protostars are embedded. We wonder if all of the molecular clouds are filamentary. If not, what are the number and mass fractions of filaments and nonfilaments? What are the different characteristics between the filament and nonfilament clouds? Is there any connection between them? These questions are still open.
In this talk, we use an unbiased catalog of 18,190 molecular clouds to investigate the morphologies of molecular clouds, which are mainly classified as filaments and nonfilaments. This catalog is extracted from the large-scale, unbiased, and high-sensitive Galactic plane CO survey, the Milky Way Imaging Scroll Painting (MWSIP). Our results on the morphology fractions of molecular clouds and the characteristics of clouds with different morphologies, provide new clues for us to further understand the evolution of molecular clouds. In addition, I also introduce several case studies on the formation and kinematics of filaments, which are based on the MWISP project.