This is an idea I have mentioned
before. I've been thinking about it for a while.
Despite my
dislike of "encounter balance" as it is commonly understood (i.e., in relation to the PCs), I appreciate the need of letting the PCs know - and, ultimately,
choose - what kind of encounters they are willing to face (of course, their place we will often go awry).
Traditionally, "encounter balance" in old school D&D is not calculated in relation to the PCs, but in relation to dungeon levels. So, the third level in a dungeon has harder encounters than the second, and so on.
I have several issues with this (e.g., each dungeon should have its own tables, how do dragons live so deep if there are no apparent big entrances), but that is another subject.
Basically, B/X has TWO "encounter balance" tools for the wilderness. First, do not go unless you're level 4. Second, some terrains are more dangerous than others (although there is an good chance of finding 1d4 dragons even in settled lands...).
This is not satisfactory because it lacks the nuance of "dungeon levels" - and also because it stops levels 1-3 PCs from traveling around to get a "taste" of what to come.
The obvious solutions is analogous to dungeon levels - the farther you are from civilization, the greater the wilderness level (you are "deep" in the forest, etc.).
To avoid creating entirely new tables (something that 5e almost manages to pull off with XGtE and ToA, to some extent), we could adapt exiting tables for these idea.
For example: roll 1d20 for each hex to the nearest the nearest civilization/ safe outpost (maximum 10).
This is a percentage of "number appearing". 100% means the maximum number appears, but that will be rare. When you get "1d4 dragons" it is more likely a single dragon unless you're a few days from civilization. Smaller numbers (e.g., 10%) usually indicate a single monster (but see "what if number appearing is one", below, for alternatives).
To add some spice, 20s explode; roll again and add 10, "ad infinitum". If the FIRST dice rolled is a natural 1-2, the rule is simply ignored - roll 1d4 to find how many dragons.
Even in the safest areas there is a chance of fighting a group of powerful monsters, but it is small (also, they might be there for a reason...).
[Alternatively, if you don't want to throw that many dice, just count some of the d20s as 10 without rolling. For example, for six hexes roll 3d20+30].
What if the result is over 100%? It is up to the GM. Rolling 130% might indicate a 30% of having found an actual lair (with up to five times more monsters), or just finding five dragons instead of 1d4.
What if "number appearing" is "one" (e.g., hydra)? In this case, the percentage indicates a chance of the encounter happening at all. An hydra next to a city? Unlikely to happen. Other alternatives would include changing the number of heads or even HD for some creatures (a dragon found right next to town was undetected for being too small, ).
What about humans? Humans and maybe some humanoids, of course, are exempt from this system; they are likely to be encountered near civilization. Elves, etc., will be more or less common according to setting.
[EDIT: as suggested in the comments, maybe changing die size could serve a similar function. So, 1d4 dragons become 1d2 near civilization, 1d3 a bit further away, then 1d4 and even 1d6. Come to think of it, this looks like a more elegant solution. Maybe results that are greater than the usual maximum - e.g., rolling 6 for dragons - indicate a chance of lair].
Building a castle or keep is automatically useful, as it makes travelling less dangerous. Roads could provide a similar result (especially if patrolled), although traveling faster is useful enough.
Add modifiers to taste: greater chance of encounter near the darkest dungeons/castles, smaller chance if travelling light with a small group, more giants in the giant territory, etc.
A more nuanced version would be creating "danger zones", each adjusting number appearing. Ideally, each area would have its own danger "level" and encounters, so that we are not "balancing encounters" but "balancing encounter tables".
Not all encounters in the same table are equal, of course. Instead, as suggested in AD&D 2e, some creatures are RARER than others regardless of HD.
It is about a fictional world - not about a game of HDs.
Of course, if you're using the tables in Xanathar's (they are decent), this is even easier: maybe 1d8+hexes, with 1-4 meaning tier 1, 5-10 tier 2 and so on.
[Notice that in 5e, similarly to B/X, Pcs of level 1 and 2 might have a hard time anyway, although the difference is smaller].
Another thing to consider, maybe in future post: cities and outpost, despite being static, might have occasional random encounters of their own (or should this be part of a "disaster check" table?). that small village encountered 4 dragons when the PCs were elsewhere? It might be toast by now...
Additional reading: