As mentioned in Section 16.1, when specifying bounding coordinates and resolution, there must be an integral number of cells contained between these coordinates in each of the coordinate directions. The integral number of cells refers specifically to T cells. In the horizontal plane, bounding surfaces of constant longitude and latitude define the location of U grid points and resolution at those surfaces is given to the corresponding U cells. Resolution varies continuously between bounding surfaces and is discretized, using Equations (16.1) and (16.2), to cell widths and heights. In the vertical plane, bounding surfaces are at the top or bottom of cells and resolution is discretized to cell thicknesses as in the horizontal plane. It should be noted that in the vertical, allowance is made for a stretching factor in the last region to provide for a more drastic fall off of resolution to the bottom if desired.