toff - oh wow I didn't even think of having a key with a depth guage, that's a great idea. My thought is to have each shade represent a 5 foot depth, so that drop-off there would be 35 feet.

coyotemax - yup yup yup. What I said to toff. Good suggestion. Thanks.

RobA - Right O! I will put my quick description of how I made it in there as well. I hope there is an equivalent method in GIMP but I just don't know.