more complete the cluster sample, the smaller the corresponding uncertainties.

We thus performed an extensive compilation of all Galactic star cluster catalogs from the literature. For completeness, this compilation was initially not restricted to the ATLASGAL Galactic range; we only did it afterwards for the comparison with ATLASGAL emission and all the subsequent analysis. The catalogs are listed in the first three columns of Table \[tab:catalogs\], where we give, respectively, an ID used throughout this work, the corresponding reference, and its category according to the wavelength at which the clusters are detected: *optical*, *NIR* or *MIR*. Optical clusters are taken mostly from the current version (3.1, from November, 2010) of the catalog by @Dias2002. NIR cluster catalogs are compilations, or lists from visual and automated searches mainly performed on the 2MASS survey. MIR clusters represent the objects detected by @Mercer2005 in the GLIMPSE data, and the new clusters discovered by us using a different search method on the same survey, which were missing in the @Mercer2005 list (see Section \[sec:newglimpse\]). In our total sample, we also included individual star clusters from the literature not listed in the previous catalogs (referred to as “Not cataloged clusters” in Table \[tab:catalogs\]). A more 