Current questions and answers regarding the map editor.

I think someone else might have asked this question here before (although I looked around and couldn't find it), but still:
Let's say I created a map for myself in the editor, saved it, and there were no errors. But the problem is that I can't find it in the list of maps, either in single-player or in online multiplayer. What could be causing this, and how can I fix it? I saved it in the Maps folder, of course.