1. A method for modeling on a computer a physical region, the method comprising: receiving data that defines at least one physical characteristic of the physical region; providing a triangular mesh on a plane of a model of the physical region, wherein the mesh comprises a plurality of cells, the model includes modeled features that model physical features in the physical region; assigning a priority value to each cell, wherein the value is determined based on whether each cell is proximate to a modeled feature and a type of the modeled feature; coarsening the triangular mesh in a non-uniform manner based on the assigned priority values; and projecting the coarsened triangular mesh in a direction orthogonal to the plane in the physical region to form a prismatic grid.