1. A method for determining a process model that models an effect of one or more semiconductor manufacturing processes, the method comprising: receiving a test layout; receiving empirical data which is generated by subjecting the test layout to said one or more semiconductor manufacturing processes; receiving a set of kernels, wherein at least one kernel in the set of kernels includes a blocked-area term, wherein the blocked-area term's value at an evaluation point in the test layout is associated with a blocked area at the evaluation point; and determining, by computer, the process model using the test layout, the empirical data, and the set of kernels by: representing the process model as a sum of product terms, wherein a product term includes: a kernel in the set of kernels; and a coefficient in a set of coefficients; fitting the set of coefficients to the empirical data; and storing the set of coefficients in a computer-readable storage medium.