what are the seven ways to portary depth or distance on a 2-d surface?

Answer 1

http://www.google.com/search?hl=en&lr=&q=portray+depth+distance+on+2d+surface&btnG=Search&aq=f&oq=&aqi=
Most of these links seem to be referring to maps, but the ideas can apply to other types of drawings, too.

Answer 2

Here is an article that might be helpful.

http://www.members.cox.net/dagershaw/lol/VisualDepth1.html

However, it doesn't even cover linear perspective.

I hope this helps a little more. Thanks for asking.