1. A computer-implemented method of modeling spatial correlations among a set of devices, the method comprising: assigning a set of physical coordinates to each device in the set of devices; representing one of a process parameter or an electric parameter for each device as a sum of at least two stochastic terms, wherein the at least two stochastic terms are chosen to satisfy the spatial correlations; simulating formation of the set of devices using the physical coordinates and the at least one of the process parameter or the electric parameter; and obtaining statistical properties of the set of devices from the simulation.