...
Iso lines are created for triangles and quadrilaterals when the isosurface visualization is selected. Their visualization can be enabled or disabled with Options --> Iso-surfaces --> Show isolines
Iso surfaces are supported for results defined over nodes or gauss points.
If the gauss points results can be globally smoothed, then a Smoothed sub-menu will be added with a list of the gaussian results, see View results menu
These isolines can be switched on and off with the command Results --> IsoSurfaces --> DysplayStyle --> ShowIsolines on the right buttons menu .
...