Menu: View results->Iso surfaces
Toolbar: 
Here a surface is drawn that ties a fixed value inside a volume mesh; for surface meshes a line is drawn. To create isosurfaces iso-surfaces there are several options:
- Exact: After choosing a result or a result component of the current analysis and step, you can input several fixed values and then for each given value an isosurface iso-surface is drawn.
- Automatic: Similarly, after choosing a result or a result component, you are asked for the number of isosurfaces iso-surfaces to be created. GiD calculates the values between the Minimum and the Maximum (these are not included).
- Automatic Width: After choosing a result or result component, you are asked for a width. This width is used to create as many isosurfaces iso-surfaces as are needed between the Minimum and Maximum defined values (these are included).
Iso lines are created for triangles and quadrilaterals when the isosurface iso-surface 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 --> ShowIsolines on the right buttons menu .
Go to Preferences --> Postprocess --> Iso surfaces to set and manage isosurface iso-surface options, like the colours colors used, style which with the isosurfaces iso-surfaces are drawn, etc. Iso surfaces