The styles splot with lines and splot with surface both generate a surface
made from a grid of lines. Solid surfaces can be generated using the style
splot with pm3d. Usually the surface is displayed at some convenient viewing
angle, such that it clearly represents a 3D surface. See set view (p. ).
In this case the X, Y, and Z axes are all visible in the plot.
The illusion of 3D is enhanced by choosing hidden line removal. See hidden3d (p. ).
The splot command can also calculate and draw contour lines corresponding
to constant Z values. These contour lines may be drawn onto the surface
itself, or projected onto the XY plane. See set contour (p. ).