  The propagation of Galactic Cosmic Ray nuclei having energies between 100
MeV/nuc and several PeV/nuc is strongly believed to be of diffusive nature. The
particles emitted by a source located in the disk do not pervade the whole
Galaxy, but are rather confined to a smaller region whose spatial extension is
related to the height of the diffusive halo, the Galactic wind and the
spallation rate. Following the pioneering work of Jones (1978), this paper
presents a general study on the spatial origin of cosmic rays, with a
particular attention to the role of spallations and Galactic wind. This
question is different, and to a certain extent disconnected, from that of the
origin of cosmic rays. We find the regions of the disk from which a given
fraction of cosmic rays detected in the Solar neighborhood were emitted
(f-surfaces). After a general study, we apply the results to a realistic source
distribution, with the propagation parameters obtained in our previous
systematic analysis of the observed secondary-to-primary ratios Maurin et al
(2002). The shape and size of these f-surfaces depend on the species as well as
on the values of the propagation parameters. For some of the models preferred
by our previous analysis (i.e. large diffusion slope $\delta$), these
f-surfaces are small and in some extreme cases only a fraction of a percent of
the whole Galactic sources actually contribute to the Solar neighborhood Cosmic
Ray flux. Moreover, a very small number of sources may be responsible for more
than 15 % of the flux detected in the Solar neighborhood. This may point
towards the necessity to go beyond the approximations of both homogeneity and
stationarity. Finally, the observed primary composition is dominated by sources
within a few kpc.
