  Blazars, a beamed population of active galactic nuclei, radiate high-energy
gamma-rays, and thus are a good target for the Gamma Ray Large Area Space
Telescope (GLAST). As the blazars trace the large-scale structure of the
universe, one may observe spatial clustering of blazars. We calculate the
angular power spectrum of blazars that would be detected by GLAST. We show that
we have the best chance of detecting their clustering at large angular scales,
\theta >~ 10 deg, where shot noise is less important, and the dominant
contribution to the correlation comes from relatively low redshift, z <~ 0.1.
The GLAST can detect the correlation signal, if the blazars detected by GLAST
trace the distribution of low-z quasars observed by optical galaxy surveys,
which have the bias of unity. If the bias of blazars is greater than 1.5, GLAST
will detect the correlation signal unambiguously. We also find that GLAST may
detect spatial clustering of clusters of galaxies in gamma-rays. The shape of
the angular power spectrum is different for blazars and clusters of galaxies;
thus, we can separate these two contributions on the basis of the shape of the
power spectrum.
