  By collecting the information from 24 previously published lists and
catalogs, we produce a comprehensive catalog (Master Catalog) of 1442 Galactic
HII regions. For each object, we quote the original fluxes and diameters as
well as the available information on radio line velocities, line widths and
line temperatures and the errors on these quantitities. References to the
original works are also reported. By exploiting all these data we produce a
Synthetic Catalog of fluxes and diameters (with corresponding errors) at 2.7
GHz. This choice is motivated by the extensive, although not complete,
information available at this frequency, widely spread among many different
catalogs, and by its relevance for both detailed studies on Galactic HII
regions and the extrapolation up to millimetric wavelengths. The catalog can be
used for detailed studies of Galactic HII regions and, by extrapolation, for
investigations of HII regions up to millimetric wavelengths. In particular, we
discuss the study of the effects of microwave emission from HII regions on the
new generation of Cosmic Microwave Background (CMB) experiments. We present
simulations of the detection of HII regions in the high resolution CMB survey,
and briefly analize some of the typical applications of our catalog to the
evaluation of CMB anisotropy experiments such as calibration, beam
reconstruction and straylight effects. The Master Catalog and the Synthetic
Catalog are available via ftp at: cdsarc.u-strasbg.fr. This work is related to
Planck-LFI activities.
