Surface plots are generated using the `splot` command rather than the `plot` command. The style `with lines` draws a surface made from a grid of lines. Solid surfaces can be drawn using the style pm3d. Usually the surface is displayed at some arbitrary viewing angle, such that it clearly represents a 3D surface. 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 or depth-sorted surface elements. See hidden3d and the depthorder option of pm3d. 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 contour.
An important special case of the `splot` command is to map the Z coordinate onto a 2D surface by projecting the plot along the Z axis. See `set view map`. This plot mode can be used to generate contour plots and heat maps.