That was just an example image, I assumed you would use your own. And actually it can be even simpler than the example I gave. The Default Shader is technically unnecessary if you attach your Image Map Shader directly as the Surface Shader of your Plane, then enable Displacement in the Image Map Shader itself (Displacement tab).
Since you want to use a procedural (fractal) terrain, you can use a similar approach. Just create your fractal terrain and attach it as the Surface Shader of the Plane object (in the settings of the Plane object node).
If you already had a fractal terrain you want to use, you can copy/paste the Plane object setup from the project here into your project by just selecting the Plane node in the node network and pressing Ctrl-C, then use Ctrl-V to paste into your own scene (in the node network). Alternatively you can create a Clip File from the plane object by selecting it and going to the File menu and using "Save nodes as clip file". Then you can easily load that clip file into any scene using Insert clip from File.
As a general note, the Default Shader's "Displacement Shader" input can use any shader that provides *color* output, and it uses the color values to drive the displacement. You will find that some shaders do not provide color, only *displacement* on their own. An example of this is the Alpine Shader. So the above approach where the Default Shader is eliminated and you just plug your fractal terrain directly into the Surface Shader of the Plane is going to be better and easier.