In one dimension, the concept of a mesh is a bit difficult, however in two and three dimensions it is vital to finite difference methods. The one dimensional method used a uniform step dx, and in the two dimensional method we will again use a uniform step h=dx=dz in both directions as in Figure 10.
Figure 10: Two Dimensional Mesh.
The continuous velocity function 
is
discretized into an average value to each square of the mesh and
is assumed to be an appropriate approximation.
This assumption is valid if h is small compared to the
wavelengths of propagation.
