Step 2: Modifying the height field.
Open the greyscale map in Gimp. In order to increase the contrast and make the elevation effects stand out more it is necessary spread the grey map over the full range of black to white. To do this open the levels window (Colors>>Levels). The levels window is likely to look something like the first screen shot.
Pull the sliders inward to coincide with the beginnings of the curves on the graph as shown in the second screen shot.
Once you hit OK the result should have higher contrast and look something like the third screenshot below.
Torq