Which map editing tool are you using?
I'm using GTKRadiant.
Cool. Power to the game mappers here
Anyhoo, if you are just outputting your map as a raster image for importing into your map editor for geometry genneration, my suggestion would be to do the following:
*In Photoshop, start with a 50% grey canvas, and paint-on detail.
OR, if you must do it in Maya,
Create a nurbs plane with reletivly high tessilation, and use the paint (artisan) tool to create your "hills and valleys" geometry.
Then, on another "Highend" 3d site, like SM, download a shader called: "Yuya Depth Shader".
Apply that to your plane, and render it from the top viewport
The problem with using the HeightField node (i.e. for Ocean shader use etc.) is that it doesn't render.
t is merely a low-res representation of your final ocean-look.
It "CAN" use an image as height input, but if you already made one for it, why use it?
So, to be blunt, for the most control, either:
1. Paint it by hand in Photoshop or,
2. Use Artisan with a nurbs plane.
Those are my suggestions, and there are other types of terrain editors specificly tailored for this type of thing like "Terregen". etc...
Israel "Izzy" Long
Motion and Title Design for Broadcast-Film-DS