I'm strongly considering running a sandbox campaign the next time I DM.
Sounds good!
I've started to brainstorm on some ideas but one thing that always throws me for a loop is how big "the map" should be. Obviously I'm not going to map out the whole world but is there a good rule of thumb for sizing the campaign area?
For an entire campaign the map should be at least 10 levels large, but you can probably get away with 3 or 4 to start. For an overland dungeon map the slowing of PC travel is far less than in city or underground dungeons. Try and estimate how far the PCs could travel in one session from the campaign starting point and expand out at least that far. This will not typically be a circular map because of the nature of the surrounding terrain. Mountains slow things up considerably, but roads, paths, rivers, waterways, and open water can extend the map considerable distances (because of potentially faster travel methods). So a prepared map will likely look oblong in consideration of terrain type. Remember the deeper the PCs travel into the dungeon (lvl 1 at starting point terrain, lvl 2, say, forest terrain, etc.) the longer it is going to to take them to move into a particular territory because of creatures / challenges therein. So don't worry about making, maybe, level 4 and above for the campaign start. That may mean you have some "hollow" giant forests and mountains where only the foothills are populated, but this allows for building between sessions according to the Players' actions.
The second question is how detailed the scale should be. Should each hex represent 1 mile, 5 miles, 10 miles? Realistically, at what point will the world seem too "cluttered"?
My advice? Do
not think of the world as needing to be gridded or hexed (like the Wilderlands map) where every river, shoreline, and road follow the hexes. Plastic overlays with hexes printed on work just as well for figuring out distance measurements on a hand drawn map as pre-hexed/gridded maps. Plus, free hand allows for greater design freedom and the essential penciling of the map (essential because all maps change as the game is played). For distance in your Legend, I think 1"=24 miles is best, but it all breaks down to terrain again and the penalties each has upon movement. 24 is divisible by 1,2,3,4,6,8, and 12, but 30 has 1,2,3,5,6,10, and 15. So it's more of a matter of what fractions are on the terrain table you are using. I *believe* AD&D used 24 miles in the DMG1e, but I can't remember for sure.
EDIT:
In terms of cluttering, it depends upon how large you want to make your early levels. Remember, the game world starts in equilibrium, so for every enemy populated area you will need equivalent neutral and ally dungeons. In standard D&D cities and towns are allies, wilderness is neutral, and underground dungeons are enemies. Personally, I would make the enemy territory about twice as large in terms of XPs as a large PC party needs to gain the next level. This includes treasure (resources). Whatever rule you make for this proportion, give the other two factions the equivalent abstract amounts and place lowest level territories of differing alignments next to each other. Like pawns on the chessboard, the borderlands are where the 1st level PCs begin. The potentially powerful allies and opponents lie farther afield.
What is a realistic area of a creature's hunting territory?
Each creatures is going to be different, but I've found it is best just to keep territory to the level or levels they are on. As with an underground dungeon, a single level may be divided up into separate territories too because of alignment conflicts. And, of course, the level they populate is based upon the Environment listing in the MM, which denotes terrain type for each creature's territory.
How far should towns and cities be away from each other?
They can be as far as whatever rule you want to make up for this. Typically towns and cities are one day's merchant travel away from at least one other. Basically, the distance a merchant wagon or vessel can travel. Civilized / Lawful population centers are almost always connected by man made constructions like roads extending this distance because of the speed gained on them. Neutral population centers may or may not have roads. Neutrals do not purposefully construct such. Paths, like those neutral animals create through accident, are used, but typically these only lead to natural resources. Uncivilized / Chaotic centers are really based upon whatever organized center already existed before they arrived.
How far will a common folk's knowledge of the surrounding area be?
Any creature is only going to know the territory they are within. They will also have historic knowledge of territories they were in, but that is only useful for knowing what was there. Which is certainly better than nothing.
Will they know about far-away places, ruins, rumors, etc?
When mapping information I find it is easiest to aggregate by faction and territory before specifying named NPC's knowledge. Information that has reached a territory will likely be known, in a town for example, by all 0-level adult NPCs who live there. Information spread only through a faction will be different, but this is still limited by territory. It's important to have rules for how information spreads, so the map can be altered as the game progresses. Given magical communication spells rumors don't just spread on foot.
I probably should check out some campaign modules, like the aforementioned Lost City of Barakus and Rappan Athuk, for some ideas on distance and scale.
LCoB isn't bad, but some things (like the area to the South and beyond the seashore) definitely need to be prepped before running. RA is more of a typical underground dungeon where all the above advice applies just as much, but it is an enemy territory to the PCs (unless you are playing a chaotic campaign?) So it would need at least as much Neutral and Civilized territory beyond its front lines (the dungeon entrances) as is in the module itself.
