Help with elevation?

[KiwiRose]

I've been drawing and painting maps for years, but only recenlty have I bothered to try and make my stuff more realistic- at least in terms of where everything goes. River direction/location, elevations maps, et cetera.

I've seen several elevation/height map generators around the forum, but how does one go about making an elevation map for a pre-existing map? I do realize there are likely a variety of methodst. While not opposed to randomized elevation on an existing map, I'd prefer some level of control over it.

Where do I start?

Edit: I currently have access Photoshop CS 6, Filter Forge 3.0 Pro and Fractal Mapper. I'm also going to play with Wilbur, but I figured I'd ask while I tinker.

[waldronate]

It may sound overly simplistic, but it's basically just draw in colors of gray. Draw the ocean in black (or a very dark gray), the solid-filled coast in a medium gray, and mountains in white (or very light gray). Then blend as appropriate (I have seen the smudge tool used to good effect for pushing things along river canyons, for example). The more gray levels you get in there, the better the final result is likely to be, assuming that you've done a plausible job of placing things in the first place.

http://www.cartographersguild.com/ho...made-maps.html has a basic discussion for using Wilbur to create simple black and white masks for coastline, mountains, and rivers.

http://www.cartographersguild.com/tu...ght-place.html offers good suggestions for getting rivers and their good buddies, mountains, where they would plausibly be for a physics-based scenario. The most important rules? water flows downhill and water erodes rocks, moving the resulting sediment downhill with it.