  We perform cluster aggregation simulations to model the structure of
anisotropic aerogel. By biasing the diffusion process, we are able to obtain
two distinct types of globally anisotropic aerogel structures which we call
"nematic", with long strands along the anisotropy axis, and "planar", with long
strands in planes perpendicular to the anisotropy axis. We calculate the
auto-correlation function, the structure factor, and the angular dependence of
the free-path distribution for these samples. The calculated structure factor
from simulated aerogels can be compared with data from small-angle X-ray
scattering (SAXS) of lab-grown aerogel allowing us to classify the spatial
structure of the lab-grown samples. We find that the simulated "nematic"
aerogel has a structure factor consistent with lab-grown, axially-compressed
silica aerogel while the simulated "planar" aerogel has a structure factor
consistent with lab-grown "stretched" silica aerogel. Unexpectedly, compressing
previously isotropic silica aerogel leads to the formation of long strands
along the compression axis while stretching silica aerogel leads to formation
of planes perpendicular to the stretching axis. We discuss the implication of
this determination on experiments of superfluid $^3$He in anisotropic aerogel,
in particular the orbital analog of the spin-flop transition.
