  We study the effects of substructure on the rate of dark-matter annihilation
in the Galactic halo. We use an analytic model for substructure that can extend
numerical simulation results to scales too small to be resolved by the
simulations. We first calibrate the analytic model to numerical simulations,
and then determine the annihilation boost factor, for standard WIMP models as
well as those with Sommerfeld (or other) enhancements, as a function of
Galactocentric radius in the Milky Way. We provide an estimate of the
dependence of the gamma-ray intensity of WIMP annihilation as a function of
angular distance from the Galactic center. This methodology, coupled with
future numerical simulation results can be a powerful tool that can be used to
constrain WIMP properties using Fermi all-sky data.
