In typical applications the value of the 
-coordinate varies less than the
value of the 
-coordinate at the north (N) and south (S) boundary, and
varies less than at the east (E) and west (W) boundary. Motivated by
this fact the points are distributed at the boundaries, such that 
varies
linearly along the -axis for the N/S boundary (where 
is constant),
and varies linearly along the -axis for the E/W boundary (where
is constant) (see Figure 3.3-7, left).
This approach fails when the N/S boundary shows excessive variations
in the -coordinate or, accordingly, when the E/W boundary shows
excessive variations in the -coordinate, for instance when using a
'U-type' grid for a trench as it will be done in
Section 3.7.1. Universally applicable is the alternative
approach, where the grid points are distributed such that varies
linearly along the arc length of the N/S boundary and varies
linearly along the arc length of the E/W boundary.
In Figure 3.3-7 both approaches are applied to a structure typically occuring during recessed oxidation processes. The grids shown in the interior of the domain were obtained by an algebraic method.
