In this talk I will introduce the three main projects of my PhD thesis.

The column density distribution of MCs has been found to be sensitive to the relevant physical processes. I will present the first study of the relationship between the column density
distribution of molecular clouds within nearby Galactic spiral arms and their evolutionary status.

A large fraction of the Galatic star-forming activity takes place inside parsec-sized filaments within MCs. However, recent studies have discovered massive, hundred-parsec-scale filaments that may be connected to the large-scale, Galactic spiral arm structure. I will present a census of Giant Molecular Filaments (GMFs) and determine their basic physical properties, analyzing also their play in the Galactic spiral structure.

Finally, I will introduce a novel absolute calibration technique for the Herschel. This technique will ultimately provide a uniform and consistently derived set of N(H) & temp maps for the entire Galactic plane. This will be a critical data-set for expanding studies outlined above to the range of environments in the Galaxy.