1. A method for estimating a spatial characteristic of an integrated circuit (IC), the method comprising: calculating a correlation between a dimension of a photoresist layer and exposure to a scanning electron microscope (SEM) for at least one reference IC pattern in the photoresist layer, the correlation providing a relationship between the dimension of the photoresist and the spatial characteristic, wherein the calculating is based on: at least one measurement derived from an SEM image of the at least one reference IC pattern produced from reducing the dimension of the photoresist layer with the SEM from an initial value to a reduced value, the initial value of the dimension, and the reduced value of the dimension; and estimating the spatial characteristic of a target IC based on the correlation.