How to Map a Fictional World

There was a time, back when I was in middle and high school, that I would sit down with a blank piece of paper and have fun drawing imaginary coastlines, mountain ranges, forests, and other items.  A little later I got some software that could help me to do that; but it still boils down to your imagination and -- if you want a "realistic" and believable world, some knowledge of geography helps.

Of course, I tend to write stories set in our modern, contemporary world.  This cuts down a lot on my need to generate maps.

I do, however, make up small towns and other far, out-of-the-way locations for parts of the story to take place in.  I do this, generally, by loading up Google Earth and zooming around the broad, general location that I'm looking to have the story take place in.  I try to find an open expanse (i.e., one with no real town in) unless I want to try to write about a town I've never been to ... sometimes I do.

For the bulk of most of my stories, the action takes place in large cities, places like New York, Philadelphia, and London.  It's easy to work with these, since maps of those cities are available at book stores, online, and even in encyclopedias.

Do you make up maps?  How do you decide on how things should look?  Or are you like me and take the "cop-out" of setting things in real places?