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 \gtrsim 10 \degr , where shot noise is less important , and the dominant contribution to the correlation comes from relatively low redshift , z \lesssim 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 .