Mapping the Wilderness: A Matter of Scale
In old D&D, a party moves through the wilderness at a pace derived from the slowest character's Full Move—namely, Movement Rate (in feet per turn) divided by five equals miles per day. In practical terms, this will usually be 120', 90', or 60' per turn, which equates to 24, 18, or 12 miles per day; or, in leagues, 8, 6, or 4 leagues per day. Just from these numbers, you can see that a scale of about a league per hex is ideal for when the party actually travels through the wilderness. (I wouldn't use two leagues per hex, because that makes it harder to account for terrain and other scaling factors that can alter travel speeds by thirds as well as halves.)
Using a typical sheet of 8½" × 11" graphing paper and 0.2" diameter hexes, the dimensions of a region map will be about 42 × 55 hexes, which is 42 × 55 leagues, or 126 × 165 miles (i.e. about 20,000 square miles of area).
I also like to scale the map once in both directions: that is, once I have my 1 league per hex scale map ("mid-scale"), I like to "zoom in" and turn that one map into nine adjacent 1 mile per hex maps ("large-scale"); and also to zoom out and sketch a wider region at a scale of about 45 miles to the inch (which would make our one league per hex area map the center ninth of this one; this map, showing the widest area, is "small-scale"). The small-scale region map doesn't need to be terribly detailed and probably doesn't even need to use hexes, but it's nice to have it for context.
So when all is said and done, there will be eleven wilderness maps: (A) the small-scale region sketch, (B) the mid-scale area map which will be used for play, and (C) nine very detailed, large-scale one mile per hex maps for the referee to reference at need. If the scope of the campaign looks like it is going to expand beyond the area map (the middle one in dark red in the figure above), any of the other eight adjacent areas within the region map (left, in black) can then receive the same treatment and become area maps in their own right. But this generally doesn't need to happen until the players are higher level and starting to eyeball stronghold construction and dominion rulership.
I always have the greatest difficulty mapping towns, because they're just not that interesting to me. Towns are the points of safety and civilization and ordinary, everyday mundanity—beacons of Law, shining in the sea of Chaos. Even if you give your towns fantastical or supernatural elements to make them flavorful and interesting, they're still always going to be less interesting than wilds and dungeons.
Ant any rate, since most towns and villages on a frontier aren't going to be laid out on a grid, I like to use hex paper instead of square graph paper for town maps as well. For these, I'll generally take normal hex paper and then superimpose some larger hexes in darker lines, like so:
This way, we can say that a large hex is a tenth of a mile across (for a small town or village) or a twentieth of a mile across (for a hamlet or thorp) and use the smaller hexes to measure local distances in feet or yards.
Since this campaign is going to take place around a thriving boomtown, I'll be mapping it out on the smaller scale, a tenth of a mile to the big hex and a hundredth of a mile (52.8 ft/17.6 yds) to the small hex. Any other small settlements in the area will probably use the lager scale of one twentieth of a mile to the big hex.
Mapping the Dungeon and Ruins
Just some more of my own idiosyncratic terminology first: I use the word "dungeon" exclusively to refer to big, multi-level complexes: "mega" dungeons. I tend to use "ruins" when I'm speaking of smaller, one-to-three-level "mini" dungeons. Hence, a campaign must have at least one dungeon—the dungeon—and it will also have many ruins (and tombs and lairs and other self-contained sites where encounters might take place) spread throughout it.
Obviously, each lair/tomb/ruin is going to need its own map (or maps, if it has a few levels). Some of them will only need a page of map and description; others are practically module sized. Underground ruins are mapped on the same 10' scale used for dungeons; outdoor maps might use a 10' scale or a 10 yard scale, depending on the circumstances. But they will all pale in comparison to the dungeon.
The dungeon will have at least a dozen levels or sub-levels. I like to have upwards of two dozen if possible—sub-levels, I mean. It's not that the dungeon will be twenty-four levels deep, with each level stacked one atop the other. Rather, the dungeon might be, say, eight floors deep, and each floor has on average three distinctly themed sub-levels.
This, in turn, serves to highlight the importance of the dungeon cross-section. As a referee, you absolutely cannot do without some visual representation of the overall shape of your dungeon. A 2D "side-view" cross section is often adequate to the task, but an isometric dungeon plan is even better. The problem is, an isometric dungeon schematic can often be quite hard to draw, especially if there are lots of levels scattered about irregularly in three dimensions, and so it's usually a good idea to construct both a 2D cross-section and a 3D schematic at the same time if you can manage it, like so.
A complete campaign needs a metric fuck-ton of maps. Region, area, sub-area, town/village, tomb/ruin, lair and other wilderness encounter, dungeon cross-section/schematic, and dungeon floor-plans. In a way, the campaign is maps: old-school D&D is a game about exploration, and the main activity is the players trying to find out what's on the referee's secret maps and to reproduce them as closely as they can. Clues and mysteries and plots and treasures and experience points are all just incentives serving to make all of the exploring and mapping as interesting as possible. Everything serves this one basic end.
Gygax is often quoted as famously having written, "you cannot have a meaningful campaign if strict time records are not kept". It is even more true that you cannot have a meaningful campaign if the maps are not drawn and populated before play begins: this is the sort of thing that you cannot make up on the fly and must never move around or alter after the fact so as to negate the players' agency. The world is the world, or else you don't really have a game, just the illusion of one.
Next time, we'll get into the nitty-gritty of actually drawing the region map. Bust out the hex-paper, kids—this is where the fun really begins!