Is there a good guide on terrain topography creating?

Question

I want to create a map for my level, and to make it look realistic from topographical pont of view. Is there anything that you can recommend?

Edit: I want to create a 3D map of islands, sea, volcanoes, shores, that will look natural.
Suppose that I want to write the map generator by myself.
Are there any resources on natural land topography?
Examples :

• The sea level should be the same anywhere.
• Sand should be near the shore.
• There is no way that there will be a huge mountain in the middle of the shore

Answer 1

The best resource I've ever read on this subject is the following article written by Amit Patel:

http://www-cs-students.stanford.edu/~amitp/game-programming/polygon-map-generation/

Here's a 2D picture of this technique:

And a 3D version of it:

I think the results are stunning. You can also try a demo here. All credit goes to Amit of course.