When I was a kid I was forever burying things in the backyard and drawing treasure maps to them. I never got tired of playing pirate, and thanks to the ancient Egyptians, National Geographic's articles on archaeological digs, plus all the divers and expeditions endlessly scouring the waters around South Florida for sunken Spanish wrecks, I always had plenty of inspiration for my map-making, too.
Mapping your fiction can be as much fun as making those treasure maps from childhood, and provide valuable insight into your world. You can also map anything, from the floorplan of a single room to an entire planet; there are no rules or boundaries in fictional cartography. Nor do you have to be a professional-level map-maker, and if you can't draw there are plenty of sites online where you can generate maps to print out.
Before we get to the how, let's talk about the two primary types of fiction maps: 1) real-world and 2) imagined world. If you want to map a location that already exists in the real world, your work will be very minimal. Do a map-image search for your location (i.e. map of downtown San Francisco) and print out the one that provides the info you need (street names, landmarks, topography etc.) When I needed to put together a mockup of Toriana for the promotional video, I simply used a silhouette of the U.S. and marked three cities whose names were different in my alternate universe:
This seems like a ridiculously simple map, which it is, but my point in making it was to show readers real-world references to three of the locations most often mentioned in the story. In a case like this, the simpler the map, the better.
The maps I draw as references for myself I most often put on graph paper, like this one:
This is the floorplan of a warehouse from my novel Nightborn, which I drew before I wrote the scene so I could work out the rather complicated choreography of the action that takes place in it. Once I knew where everything was, and how each of my characters would move through the location, it was a very simple scene to write. Mapping out a floorplan can be very valuable that way, as it gives you a real sense of the fictional surroundings your characters must deal with and/or use during any scene.
If your world is invented, you also have to create a map from scratch, which is a bit more work than using a real-world location. You're basically starting with a blank page, but in your mind there exists a concept of your location. The trick is to translate your vision onto paper, like this:
This is a map I drew of my fantasy world of Ravelin. It's nothing fancy, but it gave me the chance to work out where all the cultures and species exist. Because Ravelin's inahbitants are at roughly a medieval-level stage of evolution, their cultures are still fairly isolated from each other, although they're beginning to explore beyond the boundaries of their own lands. Before I could write those stories I needed to map out where everyone originates, name their homelands and work out their cultures (and drawing the map gave me insights into why certain species are more isolated than others, what might bring them together, etc.)
I followed no particular method to making the Ravelin map; I simply drew shapes interesting to me, applied Pangea-like logic (if the world was once all one continent, how would it have split apart over the millenia?) and let the actual shapes of the different continents and islands inspire the names I gave them. I used an Earth-like climate for my world, so the hottest areas of my world are in Tokara, at the center, while the coldest at the north and south ends. I even came up with two cultures descended from ancient outcasts -- political exiles and criminals -- whose societies evolved from their dark origins and the demands of their unpleasant environments.
If you've never mapped anything the prospect of drawing your fictional world can be intimidating, which is why it's best to keep a kid's mindset, and have fun with it. You don't have to show your maps to anyone, either; they can be strictly for your benefit (and your eyes only.)
Map-Making Resources (freeware caution: always scan downloads of free software for bugs before you put them in your hard drive.)
AutoRealm is "a Free GNU mapping software (a "cartographer") that can design maps of castles, cities, dungeons and more. AutoREALM is generally used by Role-playing Game practicants who enjoy doing their own maps. But it could fits the needs of other people. If you are a Role-Playing gamer or else, you are cordially invited to join the AutoREALM community: fellows gathered around a free hobbyist map tool. Originally made by Andrew Gryc (say "grits"), AutoREALM is now Open Source, creating a unique opportunity for the RPG world to mix graphics and computer programming" (OS: Microsoft Windows 95/98/ME/NT/2000/XP; Runs under Wine on Linux systems)
Fracplanet is an "interactive application to generate and view random fractal planets and terrain with oceans, mountains, icecaps and rivers, then export them to POV-Ray format or Blender. Written in C++ using Qt and OpenGL" (OS: unspecified)
Online Fractal Map Generator
Another Online Planet Generator
Google maps with Street View are invaluable to helping map real-world locations, and also allow you to take a visual tour of most any place on the planet.
Sweet Home 3D is "a free interior design application that helps you place your furniture on a house 2D plan, with a 3D preview" (OS: Windows, Mac OS X 10.4 to 10.6, Linux and Solaris)