Abstract
We model the Galactic distribution of the interstellar gas, cosmic rays, magnetic fields, gravitational field, supernovae, and superbubbles, based on the most recent observational data and on the requirement that the interstellar medium (ISM) be in hydrostatic equilibrium. Our model ISM will be used in a companion paper to compute the filling factor of the hot interstellar gas component as a function of Galactic radius and height.