Additionally, for points in a grid format, splot can interpolate points having a common amplitude (see set contour (p. )) and can then connect those new points to display contour lines, either directly with straight-line segments or smoothed lines (see set cntrparam (p. )). Functions are already evaluated in a grid format, determined by set isosamples and set samples, while file data must either be in a grid format, as described in data-file, or be used to generate a grid (see set dgrid3d (p. )).
Contour lines may be displayed either on the surface or projected onto the base. The base projections of the contour lines may be written to a file, and then read with plot, to take advantage of plot's additional formatting capabilities.