As I said, your terrain is procedural, as opposed to a heightfield. All you did now was export a new and flat heightfield.
What you have to do is this.
Right-click in the node network and from the menu select 'Create other' -> 'Lwo micro exporter'.
The new node (gray coloured) should have appeared somewhere near the mouse cursor.
Double-click it to change it's settings.
next to 'Filename' is a blank field and a 'save' icon. Click the icon. Browse to a folder you want to save the lwo file in, and name the file to your liking, but make sure you add .lwo at the end as that doesn't happen automatically.
Now go to the render tab of the main window. Select the renderer you want to use (eg. 'Full Render'), to change the settings.
In the lower left you have some tabs, go to the last tab called 'Sequence/Output'. If you purchased Deep+Animation you can render a sequence here, but you can also add a Micro exporter.
To do that, check the box of Micro exporter (and you can uncheck the box above that if it's checked).
Than click the '...' button on the other side of the blank field.
Go to 'Assign micro_handler' -> '"/Lwo micro exporter 01"' (the lwo exporter we just created).
Now that's done.
Last thing we need to do is place the camera in a spot that overviews the area you want to export.
The should be like the image you posted above, so that's good.
Now set the resolution to something square, like 512x512, and the render detail to 0.5.
(I once exported at full render size and detail, but the file was so large LightWave could not handle it...!)
If you have steep cliffs or overhangs, do multiple renders/exports of top and side views to capture all vertexes, as the micro exporter only creates vertexes that are visible in the render.
You can render again at higher settings with the Micro exporter box unchecked to create a top view image map if you want...
I hope you have all the information you need now.
