  We develop a powerful analytical formalism for calculating the energy density
of the stochastic gravitational wave background, including a full description
of its anisotropies. This is completely general, and can be applied to any
astrophysical or cosmological source. As an example, we apply these tools to
the case of a network of Nambu-Goto cosmic strings. We find that the angular
spectrum of the anisotropies is relatively insensitive to the choice of model
for the string network, but very sensitive to the value of the string tension
$G\mu$.
