Additionally, for points in a grid format, splot can interpolate points having a common amplitude (see set contour) and can then connect those new points to display contour lines, either directly with straight-line segments or smoothed lines (see set cntrparams). 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).
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.