Some embodiments of the invention provide a method of decomposing a design layout. The method decomposes the layout into a tessellated graph with several edges. It then computes the capacity of the edges based on a interconnect line model that is used to connect elements in the design layout. The layout has two orthogonal coordinate axes. At least one interconnect line specified by the model is neither parallel nor perpendicular to the coordinate axes. Also, in some embodiments, some of the edges are neither parallel nor perpendicular to the coordinate axes.