  We use a semi-analytic model of galaxy formation to study signatures of
large-scale modulations in the star formation (SF) activity in galaxies. In
order to do this we carefully define local and global estimators of the density
around galaxies. The former are computed using a voronoi tessellation technique
and the latter are parameterised by the normalised distance to haloes and
voids, in terms of the virial and void radii, respectively. As a function of
local density, galaxies show a strong modulation in their SF, a result that is
in agreement with those from several authors. When taking subsamples of equal
local density at different large-scale environments, we find relevant global
effects whereby the fraction of red galaxies diminishes for galaxies in equal
local density environments farther away from clusters and closer to voids. In
general, the semianalytic simulation is in good agreement with the available
observational results, and offers the possibility to disentangle many of the
processes responsible for the variation of galaxy properties with the
environment; we find that the changes found in samples of galaxies with equal
local environment but different distances to haloes or voids come from the
variations in the underlying mass function of dark-matter haloes. There is an
additional possible effect coming from the host dark-matter halo ages,
indicating that halo assembly also plays a small but significant role
($1.14\sigma$) in shaping the properties of galaxies, and in particular, hints
at a possible spatial correlation in halo/stellar mass ages.
