How Large should a Sandbox be?

[ExploderWizard]

The physical dimensions of the playing area are of less importance than the scope of player driven opportunities for activities within the game.

In order to not overprep, or be at a loss when the players want to free-range across the map just detail the area the PC's start in first. This will be the area with the most readily apparent opportunities for the players. Think about areas beyond only in the most basic ways.

1)Get a rough idea about the geographical features surrounding the start area. Don't worry about placing things on a smaller scale until needed.

2) Think about the starting area you have detailed and the civilization of that area. Do they import/export anything? To/from where? Sketchy notes at best are all that is needed.

3) Have an idea or two regarding what types of creatures live in the adjoining areas. The geography stuff along with a bestiary of some type would suffice for a sensible range of possible encounters for explorers.

4) As you get farther out the notes/ideas can get more vague and mutable.

With this model you are laying down multiple circles of definition that keep increasing in size as you step back.

This way the amount of detailed prep stays as small or large as you like and the players can roam freely.

 

[Theo R Cwithin]

To Exploder Wizard's list I'd add:

5) Have a several pre-made, but non-site-specific, encounter locations to drop in at a moment's notice-- kind of halfway between random encounters and planned encounters, if that makes sense.

IMHO, this makes the sandbox is a little more organic: the players end up guiding how the world gets built (often without realizing it, of course!). It's also surprising for the DM, as it sets up unconsidered plot arcs, unearths unexpected treasures, creates unplanned badguys, etc, which ultimately (again, IMHO) make planning further adventures that much easier.

Things like lost cemeteries or battlefields, hidden valleys, little 5 room dungeons, shrines, etc are excellent for this sort of thing.

 

[Mephistopheles]

I try to stick to the First Rule of Dungeoncraft: Never force yourself to create more than you must. Start small, with just enough in place to get things started. This kind of open-ended design allows you to respond to signs your players are giving you rather than feeling bound to things you've already invested a lot of time in creating; if a player has an interesting theory about the unexplored and foreboding Wood of Hollow Trees, an area for which you've done nothing but mark on the map and name, you're free to nab the idea and build on it - you get some free inspiration, the player gets to feel that he or she guessed right when the party gets around to exploring it (don't overdo it, and be sure you have enough smoke to obscure the mirrors).

Use a mix of hard and soft borders to keep the players from roaming outside of your designed area. Hard borders are often geographical, while a soft border is something that is at first impassable but can be broken through later - creatures that the players can't defeat or negotiate past right away, or some form of magical or other barrier that perhaps requires advancement or questing within the existing area to overcome. Soft borders are good because with time the players can overcome them and change the lay of the land, so to speak, by opening up new areas to explore. Keep a few set piece sites on hand, caves or dungeons or small wilderness adventures, in case the players go in a direction that takes you by surprise and you need to something for them to do when they get there.

The West Marshes posts on ars ludi are a good resource for sandbox style play.