  Self-organized critical models are used to describe the 1/f-spectra of rather
different physical situations like snow avalanches, noise of electric currents,
luminosities of stars or topologies of landscapes. The prototype of the
SOC-models is the sandpile model of Bak, Tang and Wiesenfeld (Phys. Rev. Lett.
59, (1987) 351). We implement this model on non-periodic graphs where it can
become either isotropic or anisotropic and compare its properties with the
periodic counterpart on the square lattice.
