Identifying the regions of open magnetic structures in the corona, namely regions where field lines expand outwards into interplanetary space, is equivalent to establishing the origin of the solar wind at the Sun. A review of recent studies, based on the comparison of the distribution, as a function of latitude, of density and velocity in the inner corona and in interplanetary space, is presented. It is shown how, at solar minimum, this comparison leads to the unexpected result that the fast solar wind expands indiscriminately from a significant fraction of the solar surface, not limited to polar coronal holes, as has been believed for the past three decades. It is also shown how polarization measurements of coronal forbidden lines, which yield the direction of the coronal magnetic field, lend further support to this result. The implications of these findings are that a significant fraction of the solar magnetic field is primarily open, expanding almost radially into interplanetary space, carrying with it the imprint of the distribution of density in the corona, while the ‘closed’ structures contribute a small fraction to the overall filling factor of coronal density structures. Furthermore, the solar wind particle flux is found to be correlated with density, implying a higher mass loss rate from the higher density quiet Sun regions, and the likelihood of a solar cycle dependence in the mass loss rate, as the are of polar coronal holes decreases with increased solar activity.