Hey dude, if you're using overviewer here's a simple step by step guide of how to compile the map (assumes Windows) as I had a nightmare finding one when i was first looking!
First off dl the latest overviewer
Next copy your overviewer files over to a folder somewhere (the closer they are to root the easier, you'll see why later) for example C:\Overviewer
Now copy your world folder over from .minecraft to the folder which contains overviewer for example C:\Overviewer\World1
Now open up a command prompt window (run then type cmd)
Type in cd directoryofoverviewer for example cd C:\Overviewer and hit return
Then type in overviewer [pathofworld] [outputpath] for example overviewer C:\Overviewer\World1 C:\Overviewer
Then hit return to run a default map build (it gives pretty good progress feedback). Of course you can customise the whole process by adding extra parameters (enter overviewer help into command prompt to see a list of these)
If all goes well, you'll have a file called index.html in your specified output directory which you can open with your browser to see the singpleplayer map (you can also update it by just following the above steps again).
I gotta say, it does seem like an overly complex/lengthy process and I'm sure some of the other ones mentioned in this thread are far more user friendly
