Thanks for the feedback.  I have experience with Paintshop Pro and Adobe Photoshop, but the concept of a grayscale elevation map is new to me.  Any advise on where to start?  I understand that white is high, black is low, but:

What size to start with?
Any limitations to observe between white and gray (min and max chroma values)?

Do you create a map just for the gross values (mountain, river, island, etc.) then import and use erosion and other filters to create realistic terrain?
 
Thanks again for the help.

Klebnor

Lotus 123 ~ S-Render ~ OS/2 WARP ~ IBM 8088 / 4.77 Mhz ~ Hercules Ultima graphics, Hitachi 10 MB HDD, 64K RAM, 12 in diagonal CRT Monitor (16 colors / 60 Hz refresh rate), 240 Watt PS, Dual 1.44 MB Floppies, 2 button mouse input device.  Beige horizontal case.  I don't display my unit.