Last column, in "Tops and Bottoms," we discussed setting creation using the technique of top down - zoom in. Following those guidelines should leave you with about 10 pages of material, including a high concept for your setting, a world map, a historical timeline of contemporary to forgotten history, and a micro-setting within your world where play is going to happen. The micro-setting ranges in size from a city (in Cyberpunk 2020) to a kingdom (in D&D) to an interplanetary region (in Classic Traveller).
Now, the astute reader will have noticed that the micro-setting from "Tops and Bottoms" is exactly the same size as the sandbox that forms the basis of the story web described in "It's Not Your Story." (If you haven't read that column, check it out here.) No coincidence, of course, because they're the same thing! The goal of the top down - zoom in method is to give you the coherent framework you need to plausibly populate your sandbox and build your story web. I call the detailed write-up of the sandbox and story web a "Gazetteer," in homage to the classic Dungeons & Dragons Gazetteer supplements such as Principalities of Glantri and Orcs of Thar. It's to that we turn our attention today.
If you're running a fantasy campaign, the sandbox/micro-setting is going to be a frontier or unexplored wilderness. If you are playing Classic Traveller, it's going to be one or two sub-sectors of star systems. For Call of Cthulhu, it might be a map of London circa 1929, for Cyberpunk 2020 a map of your home town in 2020. Since the dominant rules and favorite settings of most gamers are fantasy, I'll use that as illustrative for this column, but the same general principles apply to other settings.
Start With Static
Start with a hex map, roughly 30 hexes by 40 hexes, each representing a 6-mile wide hex (30 square miles). That gives you a region 43,200 square miles. To put that into historical terms, that's a region about the size of Greece, and thus if history is any guide, seems large enough to justify a distinct civilization with its own gods, heroes, and epic adventures. You can draw this map yourself, or use any of the widely available wilderness maps from supplements such as Points of Light or the Wilderlands of High Fantasy.
Within that map, you will place 45 static points of interest. One-third of these should be settlements, towns and castles of the humans and demi-humans, while the other two-thirds (30) are dungeons, lairs, or special areas. Of the 30 dungeons/lairs, aim for 3 mega-dungeons each designed for about 6-10 sessions of play; 10 dungeons designed for 1-2 sessions of play; and 17 small lairs designed for a half-session of play, i.e. 1 encounter. Each point of interest in the sandbox initially gets a paragraph of description.
For the dungeons and mega-dungeons, you'll just describe the dungeon briefly, to be fleshed out later, but for the small lairs, you can cover everything you'll need to use it in play. For instance:
Hex #28 Lair of the Chimera - A copse of giant acacia trees rises from the steppes here, and many wild sheep, gazelle, and other animals graze on the shrubbery and fruit and water at the nearby pond. They are preyed on by a pack of 2 Chimeras (as per Monster Manual) that live in a sinkhole near the oasis. In the sinkhole, amidst bones of dead, are a leather satchel with 15 amethysts (100gp each) and 1 small diamond (1,000gp) and 2 torn sacks of gold (1,200gp total).
Note that you don't actually have to create all the points of interest yourself. In fact, doing so is an enormous time sink. What I recommend is to cobble together a few dozen of your favorite modules, lairs, and encounters from magazines, websites, and commercial products and adapt them to your setting, focusing on just a few special areas to spend your time. In my own Auran Empire campaign, I've adapted TSR's classic modules Keep on the Borderlands and In Search of the Unknown and about a dozen free One Page Dungeons.
At this point, your sandbox should have a density of about one point of interest every 6 hexes (36 miles), putting them roughly 2 days apart at historical travel speeds. With (30 x 40) 1,200 hexes in your sandbox, the vast majority of the sandbox is empty of static encounters. Some available settings, like Geoffrey McKinney's Carcosa, have actually filled up every hex of their sandbox with encounters, but I don't think that's necessarily the best use of your time, because it guarantees most encounters will go unused.
I recommend instead creating a chart of wandering encounters for each type of terrain on your map. Then, on the wandering encounter chart, for each encounter, specify a percentage chance (usually around 25%) that the encounter will actually be a "dynamic lair" encounter. Create each of these dynamic lairs in advance, similar to the static lairs above, with 1 or 2 encounters that will take about a half session to deal with. The only difference between the two is that the static lairs are pre-placed while the dynamic lairs are placed as the party travels around.