On Blender Freestyle documentation, a picture is shown with two Suzannes made of vertical/horizontal lines.
How to reproduce this effect with Blender Freestyle? Using modifiers? Custom shaders?
The contour lines are genuine mesh edges auto-generated by a Blender/Python script as described in the following blog post:
The script implements a new operator named 'Slices'. Put the script into a text datablock in Blender and run it by pressing the 'Run Script' button, and the operator will be registered. If you have an active mesh object, then running the script for the first time will apply the operator to the mesh object. Then the operator can be invoked using the spacebar search menu and looking up the 'Slices' operator. The operator allows you to change the vertical interval of contour lines.
While the original image was generated by 'slicing' the original model (as detailed in @T.K.'s answer) an alternative method is to use the compositor as described in Create Topography Map Lines.
Using the same method produces the following result for a Suzanne model :