Wow, not finding much time available, but I did find some links to sites I used when I first did the orthographic renders above. The first is terragen tutorials,
http://cwied.com/Terragen/
There is even a tutorial for adding stuctures, the only thing I did different than this tutorial is I added the structures in Leveller, using a mask, white for buildings, black for nothing, and loaded it as a selection in Leveller (after ensuring it was the same size in pixels as my terrain,) and then used the flat add brush set to varying heights in meters to get different building heights (as in the Carn Dum render) , once I was happy I exported the terrain out as a terragen ter and rendered it in Terragen with surfacing. The best way to get the top down look is to set the camera to orthographic in the camera settins, and click auto setup, then it will position itself over the center of the terrain at a height that shows the whole terrain.
Then before you render ensure you are outputting an image the same scale as your terrain,,,if it is 600x800 pixels, output 600x800, or 1200x16000, and so on. That way you get the full terrain imaged.
The other thing is to limit the effect of atmosphere you have to set the settings in the atmo panel down to about zero for haze and atmospheric blue.

The second link is to Terrasource, a link site to get the other things needed to use terragen. 94 to its best, like FEO, cam path, and so on.
Look through cweids tut's, the y explain terragen alot better than I can. and download the free files.SeerBlue