For those who don't know, a game design document is made to bring all of the creative ideas one has about a game into concrete form. It means making a lot of decisions early on so that you have direction later on, leaving you to focus on development. When working with a team, like I am, it helps make sure everyone has the same concept. The game might not follow every line spot-on, but it should end up being rather close. Here's a screenshot of my completed GDD for Quarantine: T.O. from a bird's eye view.
If you're interested, you can see the whole thing here. I'll be pulling parts from the document and posting about them as I work on those parts to keep you all in the know of how it's coming.
~ John Adam