There's also something to be said about just drawing it out in photoshop.

I like this technique because it's really easy to just grab an airbrush and make pathways and beaches and stuff.. I think it's really the best way to do it, personally. I add another level with the texture in it right above the heightmap so I can match up heightmap pathways with the textures etc.

Then I just bring it into MED (and I always write down the scale/triangle size/etc) so when I want to edit it, I can re-create the HMP in the exact same scale.

Best wishes and happy almost new year,