The Player-Drawn Dungeon Map is a Fast Travel Hack

This post is part of the Prismatic Wasteland blog bandwagon on the topic of maps.

The first mention of mapping by players in the AD&D PHB is on page 101, in the section titled THE ADVENTURE, specifically Dungeon Expeditions:

Here it is explicitly stated that the purpose of the player-drawn dungeon map is to help the party "find [their] way out [of the dungeon] and return for yet more adventuring." There is a tradeoff for mapping the dungeon, which is that movement through the dungeon will be slow. Presumably, this will result in more torches burned, more rations eaten, and more wandering monsters encountered during mapping expeditions.

Just after this, on page 102, we are told that movement through the dungeon is faster when following a map:

Dungeon movement is five times faster when following a previously mapped route. Mapping the dungeon not only allows the players to discern the route back to the surface, but also allows them to move expeditiously along that route (thus reducing the chance of encountering wandering monsters and the use of torches and rations as they retreat).

Page 102 also tells us that mapping is not possible while moving quickly, "such as when pursued or pursuing." Additionally, "light must be available to make or read a map" (infravision doesn't cut it). Marking the walls of the dungeon (as with chalk) or leaving a trail of dropped items or string is "typically useless...as they will be obliterated, moved, or destroyed by passing creatures." The monsters are onto your dirty tricks, and they're here to ensure you end up trapped in the dungeon with them.

The section on MAPPING (page 106) recommends that two players make maps to improve the success of the expedition. It also warns players to "Never become concerned if your map is not exact...As long as it gives your party an idea as to where they are and how to get back, it is serving its purpose."

This coincides neatly with A Knight at the Opera's post on Navigation Games, in which the author argues that an abstracted flowchart-style map which foregoes precise spatial dimensions in favor of relativistic relationships between rooms is the ideal form of mapping in dungeon exploration games.

The most comprehensive remarks on mapping are found in this paragraph under SUCCESSFUL ADVENTURES (page 109):

Here is the crux of the issue: a map ensures that the party will be able to return to the surface. Again it is stated that "Minor mistakes are not very important...so long as the chart allows the group to find its way out!" I will note that the use of the word "chart" calls to mind not a meticulously drafted schematic on graph paper, but something like the flowchart-style map advocated for in A Knight at the Opera's post.

Again it is recommended that two maps be kept in case one is "destroyed by mishap or monster." This is offered alongside sound advice like "In mazes always follow one wall or the other" and things I would never even consider like "[when pursued], always go in a set escape pattern if possible" so your steps can be easily retraced, and "If transported or otherwise lost, begin mapping on a fresh sheet of paper."

That last point brings to mind a room in Dungeon Module B1: In Search of the Unknown in which the party steps into a room and is teleported to another identical room without any indication that they've been transported. I can only imagine the frustration of the hyper-precise graph paper cartographer encountering this room and making a mess of their meticulously measured and sketched map. With a less precise flowchart-style map, the mapper could instead simply add a bubble labeled "teleporting rooms" and connect it to the rest of their chart as they would any other.

In the next paragraph, the value of the map in avoiding encounters with wandering monsters is made explicit:

The map serves another purpose, which is detailed in the following paragraph:

The party is assumed to have an objective, and should not stray from it. "A good referee" will try to distract them from this objective. While it is the party's job to ignore these diversions as much as possible, it is the mapper's job to record their locations so that future expeditions can investigate them. 

The mapper is in many ways the party's memory - they record the dungeon's layout not just so that the party knows where they are and how to quickly escape, but so they know what to come back to. The information they record is instrumental in setting future expedition goals. And, since the party can travel faster through the dungeon along mapped routes, they will be able to quickly make their way back to those diversions on future delves.

Of course, not every one of the DM's nefarious tools can be thwarted by simply ignoring them. The section on TRAPS, TRICKS, AND ENCOUNTERS (page 103) describes traps which confine, channel, injure, or kill characters. Most important to this subject are channeling traps, which include shifting walls and one-way doors. Mapping is suggested as a solution to these traps, as a good map allows the party to find their way back after ending up on the wrong end of one:

The following section on tricks also describes dungeon features which specifically "foul maps", similar to the teleporting rooms in B1:

Let's jump over to the DMG, where the first mention of player mapping is in the section on EXPERT HIRELINGS (page 33):

Specialist scribes (or cartographers) can be hired on a monthly basis to make or copy maps. They demand ten times the fee of a normal scribe, which is 15 gold pieces per month (150 gold pieces per month for a cartographer). Gygax tends to recommend that NPCs charge more to travel somewhere or to provide their services in a dangerous environment, so I imagine that this would be even more expensive if the cartographer is meant to join the party in the dungeon (perhaps five to ten times the usual cost, so 750 to 1,500 gold pieces per month). 

Still, this is well worth the cost if the party can afford it, as they are essentially relieved of the burden of mapping themselves. Instead, I imagine the DM would provide them with a map as they go which, since a well-paid specialist is making it by way of the DM, is probably quite accurate. Of course, a particularly cruel DM is at liberty to take advantage of this by making the cartographer unreliable in some way or by using monsters to target the party's expensive civilian escort.

Note that charmed creatures will not draw maps, per page 43:

If the party wants a dungeon map, they will either have to make it themselves or pay an expensive hireling to do it (and protect said hireling in the process). If they cannot or choose not to circumvent the challenge by paying an NPC, they will themselves have to deal with threats such as traps which channel them into unintended areas and tricks which meddle in their attempts to map. 

We have also been dancing around the issue of time, which imposes the threat of wandering monsters and resource expenditure. So how long does it take to map? The section on THE FIRST DUNGEON ADVENTURE (page 96) gives us some details. This first paragraph suggests that mapping a room or chamber takes 10 minutes:

The next paragraph suggests that each turn, the party can map a length of corridor equal to the party's base movement rate times ten:

Simple enough. However, the first paragraph is contradicted by this next one, which suggests that it takes one turn to map only a 20' x 20' area:

Or perhaps the correct way to read this is that mapping any room or chamber takes one turn, which is the same amount of time it takes to casually examine a 20' x 20' area. I'm not entirely sure.

I tend to let players map one room or chamber per turn. Obviously, this requires stopping in the room or chamber for one turn, so the mapper might update the map while the rest of the party searches the room, checks for secret doors and traps, picks a lock on a door, or whatever. I do kind of like the rule for mapping hallways as I'm never quite sure how to handle those, so maybe I'll keep that one.

There's actually a third way for the players to obtain a map of the dungeon, and that's if they find one. The sample dungeon included in this section of the DMG provides the opportunity for the player characters to find an incomplete map of the dungeon in just the second room:

The importance of this incomplete map is made apparent in the example of play which follows:

The partial map indicates to the players where there might be areas to explore (in this case, they go to Area 3). Since they know that there is an area south of this room, yet there are no exits, they suspect that there must be secret door leading south, and indeed there is.

This, of course, allows the DM to set up an evil trap involving some ghouls:

So maybe if the DM gives you a map of the dungeon in only the second room, be a little wary of where that map might lead!

While there are many benefits and perils when it comes to mapping the dungeon, ultimately the one we must come back to is this: the map helps the party move expeditiously throughout the dungeon. It not only aids the players in remembering the way out of the dungeon, but it hastens them in their egress. The map doesn't just help the players remember things to come back to later, but allows them to return to those side passages more quickly.

Regarding the former - for a player-made dungeon map to yield its true value, getting out of the dungeon without one needs to be every bit as hazardous as making progress into it. This danger is essential to D&D's resource attrition game, which must work as intended in order for the game to remain challenging without relying too heavily on cheap tricks like traps and monsters which can instantly kill the player character. 

One of the most common complaints about D&D's gameplay loop (particularly in post-TSR editions of the game in which all resources are recovered on a single night's sleep) is that the game's attrition-based challenges are too easily circumvented by abusing rests - i.e., the 15-minute adventuring day. This effect is worsened when the DM provides the players with perfect information about the areas of the dungeon they've already explored, such as if the DM draws the map for them as they go, or uses a VTT and leaves previously explored areas of the dungeon displayed on screen after the characters have left them. To rest and recover all their resources, players need only go back the way they came, which is plainly laid out for them by the DM.

If the players have to actually make the map themselves, there's a chance of them doing a poor job. Those who map poorly (or foolishly choose not to map at all) run the risk of getting lost. If they're lost, they can't leave whenever they want to recover lost resources. They may find themselves low on hit points and spells, wandering aimlessly, and easy marks for the dungeons depredations.

The players are rewarded for their efforts not only with hastened escape from the dungeon, but also with expedited travel back into it to tie up those many diversions seeded by the DM on prior expeditions. This allows them to avoid needless encounters with wandering monsters on subsequent delves, making it more likely that returns to the dungeon will be successful and ensuring that the party maintains its momentum throughout the campaign. This doesn't mesh well with modern D&D's dungeons which are seemingly designed to be cleared out in one go, but is essential for making progress in old school D&D's more megalithic underworlds.

The point of the players making the map is to make movement through the dungeon faster, but they have to make it themselves. As argued in A Knight at the Opera's post, mastering the layout of an environment like the dungeon is a perfect example of a challenge of player skill. The map is a powerful tool that must be earned. Don't give it away for free. Or, if you do, be sure to use it to lure the party into an ambush by some ghouls. That'll teach 'em.

Underwater Adventures: D&D's Forgotten Realm

Underwater adventures are grossly underutilized in D&D. Even simple nautical or seafaring adventures (where the main mode of wilderness travel is via boat rather than on foot) are relatively rare. There might be the occasional partly flooded dungeon or passage on a ship to the Isle of Dread or Chult, but little of the adventure in D&D seems to take place beneath the waves themselves.

This makes plenty of sense, as players are likely controlling land-dwelling characters like humans, dwarves, elves, or halflings. "Water levels" in video games like Donkey Kong Country, Legend of Zelda, or Metroid (to name but a few) are iconic, but often for the wrong reasons - that is, they're annoying as Hell. Presumably, underwater adventures in D&D would be likewise. 

The AD&D DMG devotes two full pages to play in these environments (which at once seems like a significant amount while also being unfathomably scant). There's a lot to consider in those two pages. There's also a lot to consider beyond them. But look at this introduction:

Ancient submarine civilizations? Creatures half-man and half-fish? Mountains of sunken loot? Pearls as big as a man's head? Beautiful mermaids? I need to go there. Why don't we go there more?

For starters, there are issues like breathing, movement, vision, combat, and spell use to consider.

 Underwater breathing can be achieved by spells, potions, magic items, or other contrivances invented by the DM for the occasion:

Since the ability to breathe underwater is time-limited, underwater adventures are assumed to be akin in scope to dungeon adventures, rather than wilderness adventures. What I'm imagining is the characters piloting a boat above some sunken ruin, casting all their spells or chugging their potions, and diving in for a short expedition. While all dungeons have time pressure in the form of random encounters and available light sources and provisions, underwater adventures take this to the extreme. If you can't get out in time, you die.

(Add "comestible" to the list of words I learned from reading D&D.)

Just as underwater expeditions are similar to dungeon adventures in terms of duration, they are also similar in terms of movement:

When adventuring underwater, characters use their dungeon movement rate. A character with a movement rate of 12" can move 120 yards per turn outdoors on dry land or 120 feet per turn in a dungeon on dry land. Underwater, they likewise move 120 feet per turn. This assumes that underwater adventures are basically "outdoors".

How quickly then does the character move in an underwater dungeon? It isn't clear. Since your "outdoors" underwater movement rate is equal to your dry land dungeon movement rate (itself one-third of your dry land outdoor movement rate), I would personally rule that your movement rate in an underwater dungeon is likewise one-third your dry land dungeon movement rate. So, a character with a movement rate of 12" would move 40 feet per turn in an underwater dungeon. Sounds pretty reasonable to me.

Swimming is only possible when the character is wearing leather armor or lighter and is carrying fewer than 20 pounds. That's not a lot of equipment! Then again, you probably don't want to get most of that equipment wet anyway. Even magic equipment like a ring of swimming does not permit swimming if these conditions are not met.

Swimming introduces another unique element of underwater adventures - swimming characters are vulnerable to attack from every direction. Underwater adventures are more three-dimensional than land adventures because, outside of flight or levitation, characters don't usually have such unfettered access to that third dimension.

This section also gives us a hint at what sorts of environments or terrain are found underwater - hills, coral outcroppings, shipwrecks, seaweed forests, and the like. Note that swimming without the aid of free action magic does not allow you to move faster than someone forced to walk along the ocean floor, but it does allow you to swim over or around these obstacles.

Next is vision:

There are basically "simple" rules for vision (you can see X' until you reach a depth of Y', at which point the environment is treated basically as darkness) and "complex" ones. (you can see X' when 10' below the surface, but X decreases by 10' for every 10' you descend). 

Underwater environments complicate infravision because the temperature of the water is varied by shifting currents. Seaweed, schools of fish, and mud can obscure vision. Sea grass can be up to 30' tall and clouds of mud can persist for up to 12 rounds!

Then we have combat considerations:

Without free action magic, only the use of thrusting weapons is possible, and natural swimmers will always strike the first blow against landlubbers unless a weapon with reach is employed. 

This is where nets (themselves the unsung heroes of the D&D weapons list) will shine. Characters can throw a net only a number of feet equal to their Strength score, and suffer -4 to hit with them unless they've trained extensively (underwater!) with the use of such a weapon. 

Specially-made crossbows costing ten times the normal amount can also function underwater. If an underwater adventure is to transition to one in an airy environment ("like the great air-filled domes of Atlantis"), bows, missiles, scrolls, and other items must somehow be kept dry.

We also get a taste of what creatures might be encountered in the water - aquatic elves, locathah, mermen, and the true terrors of the deep, sahuagin. The latter employ clever and dastardly net traps in their ambushes.

Finally, spell use:

Like most everything else, spells function as they do in dungeons, with a few caveats. Some material components will not function underwater. Fire-based spells will only function in airy water, and electrical spells will affect the entire area. I imagine it would also be difficult to make the precise gestures required by somatic components (unless magically capable of moving freely) and to speak verbal components (unless in airy water or maybe if magically capable of breathing water), but this isn't stated.

There is a sizeable list of spells that won't function underwater or will only function in airy water (marked by an asterisk):

Many of these are fire spells, but there are other notables - spells which summon insects, and spells dealing with air, wind, or the weather. Animal summoning is curious - could the caster not just summon aquatic animals instead? I imagine this is because the spells and their tables assume that adventures will be happening on land. Still it would be nice if alternative underwater tables were provided. You can't summon a cacodemon or woodland beings, but you can apparently cast monster summoning. Unlike animal summoning, the monster summoning spells do get their own underwater tables:

Also of interest is that spells that require speaking (speak with dead, speak with plants) function only in airy water, which seems to suggest that unless air is present, speaking is not possible. So then wouldn't any spell with verbal components not function without air as well? That's like, most spells. Curiously, speak with animals is omitted. 

I would probably say that if you can breathe underwater, you can speak (and utter verbal components) underwater. If you are capable of swimming (either due to being unencumbered by armor and equipment or by way of magic), you can perform somatic components. Easy peasy.

Then there are a handful of spells which are specially altered when cast underwater:

My favorites have got to be wall of ice (the entire wall simply floats to the surface) and Otiluke's freezing sphere (the caster entombs their self in a sphere of ice, which floats to the surface, and they suffocate unless freed).

This all sounds like a bit of a headache for the DM and players alike, and that's because it is. Underwater environments are alien - more alien even than the dungeon. The deep ocean is probably the most alien place on our own planet Earth. It makes sense why so few adventures take place underwater. Adventuring there should be hard, because the characters aren't from there. But what if they were?

The allure of underwater adventures, in my opinion, is not brief expeditions to sunken dungeons (although that is certainly one of the lures), it's the ancient civilizations and the creatures half-man and half-fish - the aquatic elves, locathah, mermen, sahuagin, and the like. There are vast empires (or probably more accurately in most cases, pretty large isolated ethnic enclaves) beneath the waves, and they are inhabited by all sorts of aquatic people. Can't the players play as one of those people?

Let's start by looking at the underwater encounter tables. These are broken into shallow water (where vision is relatively easy) and deep water (where light from above does not penetrate), and into fresh water and salt water. Who says your underwater adventures have to take place in the ocean?

Interestingly, the paragraph before the tables suggests that the "Number of creatures encountered should be appropriate to the strength of the encountering party":

Hmm...Here I thought old school D&D was supposed to eschew balance (which is maybe true - some true believers don't consider AD&D "old school"). While this same sentiment isn't reiterated prior to the land-based wilderness encounter tables, I can't imagine why it would apply only to underwater encounters. File this under "Important rules mentioned once in passing in a random section of the DMG".

Anyway, I will admit that the fresh water encounter tables do not suggest some larger civilization of which the player characters might be a part or might engage with. It's mostly animals and unintelligent monsters:

Hobgoblins and lizard men are certainly playable races in later editions of D&D. There are some other intelligent monsters in here like giant beavers, gargoyles, ghouls, naga, nixies, and nymphs, but none of those exactly read as playable races (though a giant beaver campaign would be sick). Interestingly, dinosaurs are on the list, despite being found on land only in "Pleistocene Settings". Even if your AD&D world overall is not populated by dinosaurs, they will still dwell in your rivers, lakes, and oceans!

The deep water table is more of the same, though it eschews a few monsters (regular crocodiles, giant frogs of all kinds, green slime, hippopotami, regular lampreys, giant leeches, and nymphs) in favor of others (giant water beetles, dragon turtles, storm giants, giant lampreys, and purple worms). It's cool that the deep lake next to town might have a dragon turtle, a purple worm, or a storm giant's castle at its bottom.

The salt water tables are a bit more interesting:

Here are the aquatic elves, locathah, mermen, and sahuagin. They are joined by ixitxachitl, sea hags, triton, and more nasty sea creatures, plus many of the same interesting creatures from the fresh water tables like storm giants, hobgoblins, gargoyles, ghouls, and nymphs. The deep water table adds the eye of the deep (a deep sea beholder) and one of my favorite weirdos, the morkoth.

Underwater environments in AD&D are full of nasty monsters that leap out of hiding to eat you, swallow you whole, capsize or sink your ship, poison you, paralyze you to be eaten, stun you with light or trick you with illusions to tear you apart with their crab claws, torture you, melt you, suck your blood, enslave you (but only for one year!), and blind you or kill you by looking at you or by getting nude in front of you.

Like many of AD&D's environments, underwater is not a nice place. But these environments are also home to intelligent beings with their own societies. 

10% of dolphins form underwater communities of 4 to 100 dolphins with swordfish and narwhals as trained guards. Storm giants live in spacious castles beneath the waves and keep sea lions as pets (for whatever reason, all of their magical abilities are those select spells which explicitly do not work underwater). Koalinth (aquatic hobgoblins) fulfill much the same function as their land-dwelling counterparts. Ixitxachitl lair in secret coral reef caves and can be clerics of as high as 8th level. Some of them are vampires. Locathah live in hollowed out castle-like undersea rocks, ride eels into battle, and use Portuguese men o' war as traps (implying the existence of Portugal in the default AD&D setting). Water naga are curious creatures capable of casting spells as 5th level magic-users.

Aquatic elves are much like land-dwelling elves (with whom they engage in trade), but they are allies of dolphins and mortal enemies of sharks and sahuagin. There are wars being waged beneath the waves! They dislike fishermen because the elves get caught in the fishermen's nets, are mistaken for sahuagin, and killed.

Mermen live in undersea communities among the reefs and cliffs, sometimes constructing villages of shells, rocks, and coral. They herd fish, have their own workshops, and keep barracuda as pets. Oh, they also form raiding parties to grapple surface ships en masse and slowly drag them down to the bottom of the sea to be looted, killing everyone aboard in the process. Huh.

Sahuagin get more than a full page all to themselves. They are devil-worshippers and dwell "in a vast undersea city" ruled by a king. The city is built in an undersea canyon lined with palaces and dwellings. 5,000 sahuagin dwell there with 1,000 queens, concubines, nobles, and guards in the king's retinue. The king rules nine provinces (mirroring the levels of Hell), each ruled by a prince. The princes live in strongholds, while most other lairs are "actual villages or towns, constructed of stone" and hidden among the seaweed. 

They align themselves with sharks, venture onto land to raid, and hate even the evil ixitxachitl. They have a matriarchal religious structure with clerics of up to 8th level. 1 in 216 (2+1+6=9?) - including the nine princes and the king - is a mutant with four fully functioning arms. Those they capture are either tortured and eaten or made to compete in blood sport, dying either way.

They are either distant relatives of the sea elves created by the drow, or some Lawful Evil god created them from humans "when the deluge came upon the earth." I'm sorry - I wasn't aware of The Deluge! This is rich stuff.

Triton live in undersea castles and sculpted caverns, can become 6th level magic-users, and keep hippocampi, giant sea horses, and sea lions as pets. They can use their conch shell horns to summon these creatures to their aid and panic unintelligent sea creatures. Some have psionic ability. They are from the Elemental Plane of Water and "have been planted on the Material Plane for some purpose presently unknown to man", engaging in wars with sahuagin, ixitxachitl, koalinths, and lacedons.

There's a lot going on underwater! It's dangerous and comes with a great many complications, so I can see why humans, land elves, dwarves, and halflings aren't exactly eager to board a ship and risk getting sunk by a dragon turtle, giant squid, or raiding party of murderous mermen, let alone actually go diving down there to contend with these horrible creatures in such an alien environment. That doesn't mean we can't have adventures there.

I could see a campaign where the player characters are aquatic elves, locathah, mermen, tritons - hell, even koalinth or sahuagin - plundering the ruins of their own ancient civilizations as well as the sunken remains of the civilization above, building undersea strongholds among the coral and cliffs, and getting mixed up in factional politics and aquatic warfare. There are still dungeons there, and dragons, too (in turtle form, at least) - the only two things you really need for a D&D campaign.

A campaign in such a drastically different environment would need to have many considerations. Being able to swim freely underwater is akin to every creature having unlimited flight. I imagine no one is wearing armor. How do potions and scrolls and spellbooks work? Have the magic-users of the undersea realms developed an underwater version of fireball that cooks you alive in a blast of boiling water? That sounds pretty neat.

I need to go there. Why don't we go there more? Why aren't we there right now?

AD&D's Domain Game: What to Learn, What to Leave, and What to Love

I'm currently in the process of trying to puzzle out how exactly "territory development" (what we would now probably call the "domain game") works in AD&D, as described on page 93 of the DMG, TERRITORY DEVELOPMENT BY PLAYER CHARACTERS:

The process begins when the player decides to establish their character's stronghold. They pick a spot, the DM provides a map of the hex and the six surrounding hexes, and the player character and their henchmen and retainers go to the place to explore it and begin construction:

In the example, the player character wishes to construct a stronghold 100 miles from a border town, although there's no indication at this time that there's any required distance (I'll get back to that). 

The DM must prepare a small scale map of the terrain in the area, 200 yards per hex. An area which is nine such hexes in width then makes up a larger one-mile hex. It and the surrounding six hexes are the area to be explored and mapped. Once they are all mapped, workers can be brought in to begin construction. A garrison has to be present to protect the workers, as each day there's a 1-in-20 chance of a monster wandering in from the area beyond these seven hexes, unless the area beyond is being patrolled:

I tried to visualize what this area would look like in Hexographer and came up with the following:

The smaller hexes are 200 yards across. The larger hexes are one-mile across. They are nine hexes across at their widest (from easternmost to westernmost vertex), so I think this is indeed what's being described in the excerpt above. Each one-mile hex contains 44 (!) 200-yard hexes.

The DM "checks but once for random monsters in each hex". Does this refer to the 200-yard hexes or the one-mile hexes? I don't know. One monster per one-mile hex sounds like plenty to me, and two monster lairs potentially within 200 yards of one another strains credulity, but wandering through 44 200-yard hexes with a chance for a monster to be encountered in just one of them seems rather droll. Indeed, this next section suggests that the DM only check for monsters once per one-mile hex after this "core area" is mapped out:

This sounds to me like, when exploring the "core area" of seven one-mile hexes, the player character explores each 200-yard hex one by one, with the DM checking for monsters (and possibly randomly determining terrain) in each one. It is only after the core area is mapped that the player character begins more quickly exploring the surrounding one-mile hexes (instead of the 200-yard hexes within), at which point monster checks are made "as is normal for outdoor adventuring" (emphasis mine).

Furthermore, once per day, the DM checks to see if a monster wanders into any one hex which borders an unexplored hex. Once per week, the DM checks to see if a monster wanders into "the central part of the cleared territory" (this I take to mean any explored hex which doesn't border an unexplored hex, not necessarily the central hex where the stronghold is being built, but I could be wrong).

Here's my attempt to visualize what this "core area" might look like (using the provided example of wooded hills, though I'm using a variation of the Welsh Piper method instead of AD&D's method for randomly determining terrain), with the hex where I think the player character might locate their stronghold indicated with a star:

According to the AD&D DMG, we're to check for encounters based on population density (this isn't what I usually do, but will for the sake of this example):

Since this area is 100 miles from the nearest border town, it's probably uninhabited/wilderness area. That means 1-in-10 of these 200-yard hexes will have a monster in them. Here's what that looks like:

That's 28 monsters. Am I doing this right? I honestly have no idea. I'm doing as described, checking each hex for a monster, not spacing them out according to any sort of logic or reason. It seems strange that the southernmost hex would have three monsters each within 200 yards of the other two, but this is what I got by following the procedure.

Again, once this is all mapped, construction can begin (the DMG does not explicitly state that the monsters have to be driven off or killed before construction can begin, unless I'm missing something), and the player character will then begin exploring the one-mile hexes surrounding these hexes, with checks for monsters proceeding according to the normal rules for wilderness exploration. 

Meanwhile, there is a chance per day that a new monster will wander into a border hex and a chance per week that a monster will wander into a central (non-border) hex. This can be prevented by signaling to intelligent monsters that the area is dangerous to them, patrolling frequently and aggressively, and by organized settlement of the cleared lands:

Once the stronghold is finished, if proper patrols are organized, only weekly checks for monstrous intruders are needed (one each on the Uninhabited/Wilderness table and on the Inhabited table). If a road is built through the area, checks are instead made on the Inhabited table three times per week:

The Inhabited table is made up of many (presumably) good (i.e., profitable) things, like dwarves, elves, gnomes, halflings, leprechauns, merchants, nomads, pilgrims, and mundane animals. It also has some bad things, like ankhegs, bandits, brigands, bulettes, giants, humanoids, lycanthropes, manticores, ogres, and all manner of undead. Thus, a domain with a road through it will more frequently be settled by men and demihumans and fey creatures, but will also more frequently be preyed upon by certain monsters and haunted by ghosts. The distinction between the Uninhabited/Wilderness table and the Inhabited table has always struck me as a neat way of modeling which monsters are attracted to human inhabitation and which ones stay far away.

The DM no longer checks for monsters from Uninhabited/Wilderness areas once a territory of more than 30 miles from the center (here I'm guessing the center hex, not necessarily the exact location of the stronghold itself) is patrolled or inhabited. That's 30 one-mile hexes that must be explored and then patrolled in all directions (961 hexes total).The monsters from the Inhabited table continue to show up and settle in the area, and the area returns to wilderness if not patrolled or inhabited:

Inhabited by whom? Well, I guess the merchants, demihumans, and fey creatures. Presumably the nomads and pilgrims are not settling, as wandering is part of their nature. I suppose homesteads will begin to crop up. These will grow into thorps, then into hamlets, then villages, then towns, and finally cities, but how exactly this transpires is left to the imagination.

The next paragraph answers the question - how far must a player character's stronghold be from civilization? Well, it needn't be far at all. In fact, it is suggested that the stronghold might be "located in the heart of some powerful state":

As is often the case in AD&D, the emphasis is on maintaining the campaign as challenging and interesting. In this scenario, the stronghold ruler is not clearing monsters from their land and then holding it against wilderness incursions, but instead dealing with "intrigue and petty wars...jealous neighbors, assassins, and the like" which threaten the fief.

Next we come right back to the matter of inhabitation of wilderness domains:

Again, once the stronghold is finished and patrols have cleared the area, inhabitants will come to settle. I think this is at the same time as when the DM begins checking weekly on both the Uninhabited/Wilderness and Inhabited tables (i.e., before the 30 surrounding one-mile hexes have been cleared and patrolled, but again it isn't entirely clear).

The inhabitants "will match the area and the alignment of the character", which is interesting. Lawful Good creatures will settle in a paladin's domain, for example. Random monsters will settle in the area, "making proper subservience calls upon the master of the territory". I imagine this means that the Lawful Good dwarves who move into the paladin's realm will become loyal inhabitants. Would the Chaotic Evil ogres who move into the Chaotic Evil cleric's realm likewise become the cleric's vassals?

Hamlets, thorps, and other settlements will begin to crop up, starting near the stronghold and working towards the fringes, but no indication is given as to how quick this settling process is, how long it takes one settlement type to grow into another, or anything like that. (OD&D, for its part, suggests 2-8 villages of 100-400 inhabitants each per territory, but it also leaves to the imagination how exactly these come to be.)

Once the settlements are established, "they can be used as centers for activity - good or evil or whatever." They "attract more of the ilk which inhabit them, draw opponents sworn to exterminate them, trigger raids or reprisals, etc." The domain game becomes less about fending off wilderness incursions and more about managing the region's inhabitants and dealing with complications that arise as a result of - presumably - the ideology of the player character and their people. The paladin will need to thwart attacks from the forces of Evil Chaos, while the Chaotic Evil cleric will be dealing with assaults from the realms of Good and Law.

What's interesting is the onus placed on actions taken by the player character - that is, "forming active groups from the population base and doing something." The DM is intended to "initiate by setting up a series of circumstances which will bear upon the territory" only as a last resort. Is that to suggest that the paladin's realm is only besieged by Evil Chaos after the paladin has instigated the conflict in some way? Do the forces of Law and Good simply not mind their Chaotic Evil cleric neighbor until his ogre vassals start plundering their land? I like the emphasis on player agency, but this doesn't make a whole lot of sense to me.

One thing that strikes me is that the domain and its inhabitants read like an extension of the player character. The regular inhabitants are all of the same alignment, pay taxes (as indicated in the class descriptions in the PHB), and exist for the player character to form "active groups" and do "something". Are we talking about raising armies? How many peasant levies can be raised from the thorp, hamlet, village, or town? It isn't clear, but clearly these inhabitants are intended as additional resources and game pieces for the player to employ in whatever their ends may be. They need to be protected, not necessarily because the character is a Good hero but because they share the character's ideology and are useful in some way.

Next, we are told that the "real benefit" of player character territories is what they contribute to the DM's milieu:

When the player character constructs their stronghold, the player should provide the DM with floor plans (including dungeons) and a map of the immediate area surrounding the stronghold. This is so the DM can plan sieges and other attacks upon the fortification:

Finally, if a player leaves the campaign or switches to a new character, the DM can take control of the former character's domain and run it as they wish:

I would be remiss not to mention the possibility of uprisings if the player characters forces peasantry, serfdom, or slavery upon their subjects:

Peasantry/serfdom is not the accepted norm for common people in the AD&D world. D&D is not medieval.

This also gives us a window into what it looks like for a player character to raise levies from the normal inhabitants of their domain. 1-in-5 of the inhabitants will be fighters (which I take to mean adults capable of fighting, not individuals with a level in the fighter class). These troops will be 0 level peasants, treated "as up to 1-1 HD" monsters according to the EXPERIENCE POINTS VALUE OF MONSTERS section of the DMG:

This means the average single dwelling (population 6.5) will yield one troop, the average thorp (population 50) will yield ten, the average hamlet (population 250) will yield 50, the average village (population 750) will yield 150, the average town (population 4,000) will yield 800, and the average city (population 35,000) will yield 7,000.

If we standardize the values provided by the DMG's INHABITATION table, that area of 961 one-mile hexes (960, not counting the hex in which the stronghold itself is located) could eventually support 28 to 29 single dwellings, 19 to 20 thorps, 19 to 20 hamlets, 19 to 20 villages, 9 to 10 towns, and 9 to 10 cities. On average, that could yield from 74,000 to 82,000 peasant levies in a new campaign or uprising. 

That seems a bit hard to believe, so I am probably over-interpreting the available information. The whole point of this section is that these people do not tolerate being subject to peasantry, serfdom, or slavery, so it seems unlikely that the ruler could call on their subjects (if they can be called "subjects" at all) in such great numbers. The numbers given also pertain to an enthusiastic uprising in which everyone who can pick up a weapon for the cause does so. Perhaps in an organized war effort the numbers should instead be cut in half. 

Perhaps the intention is for the player character to lead campaigns with only the strength of their follower armies and mercenaries, but it seems a bit hard to believe that these tax-paying settlements contain no loyal warrior subjects who can be called upon in a conflict.

In any case, if the uprising (or perhaps campaign) lasts more than a month, you add 10% to the total force for each month, and upgrade 10% of the total force to regular men-at-arms (1-1 to 1 HD monsters) and give them improved tactics. This suggests that perhaps a more warlike ruler cultivates a more warlike populace over time. (OD&D, of course, famously suggests the insertion of a Conan-type "to bring matters into line" in the event of an uprising.)

There would also eventually be two additional strongholds in the area which, since the player character's stronghold controls the area, are likely vassals or henchmen of the character, and so would contribute their own forces as well (men-at-arms as well as whatever followers are attracted by, say, a fighter or cleric). Normally some of these strongholds would be inhabited instead by bandits, berserkers, brigands, or the like, or become deserted and potentially inhabited by monsters, but since this is a newly developed territory such a takeover or ruination would have to happen as part of an in-game event.

Now, is this system good game design? I don't know, I probably wouldn't use it as is. I think it's pretty unlikely that the player will say "I want to go 100 miles away from this town and build my stronghold on some random hill, where I don't even know what the terrain is like or where monsters may be." I don't really like the idea of switching to a much finer-grained scale of wilderness mid-game and forcing the players to laboriously explore some 300 hexes and slog their way through 30 monster lairs to establish their domain, then explore and inhabit or patrol an additional 950 hexes just to stop monsters from wandering in all the time. 

More likely is that the player characters will set up their domain in some place that they're familiar with - the existing campaign area. I obviously make a lot of sandboxes, and I arrive at the first session of the campaign with a complete map of settlements, strongholds, ruins, and monster lairs. Once the player characters familiarize themselves with the area and grow in power, I think they're more likely to build their stronghold in a region that's already settled, to take a readymade stronghold from someone else, or to rehabilitate a ruined stronghold into something they can use. If there are monsters nearby, they'll have to deal with that, but I wouldn't require them to meticulously explore a huge area before they could even begin building the thing.

I do like the idea of checking regularly to see if monsters wander into the area from the wilderness, but feel that this could be applied more broadly to the campaign map as a whole. Maybe you check each unoccupied border hex of the campaign map on a regular basis to see what new monsters move into the area, and maybe likewise track their movements from one hex to another as time passes and they search for a lair to settle in. Maybe they stumble into the player character's domain and stir up trouble in their search for a home or for prey. You could have some sort of minigame for when the monster wanders into a patrolled area to see if the patrol can handle it or if the monster overwhelms them and continues on its march.

I really like the image of a player character's (or NPC adventurer's) territory being surrounded by monster carcasses and totems to ward off intelligent monsters. When the player characters see that, they know they're entering into some powerful NPC's domain.

I also like that different types of monsters are drawn to strongholds more frequently if they're joined to the rest of civilization by a road. Building a road between the stronghold and the nearest settlement is a matter of great convenience, allowing expedited travel back and forth. It will attracts merchants and elves and dwarves to the domain, but it will also attract all the men and monsters that prey upon civilization. 

I like the distinction between wilderness domains and those within settled regions. Do you want to deal with monstrous incursions, or politics and intrigue? Would you rather defend against the occasional orc warband wandering into your domain, or with the neighboring warlord's organized campaign, a king somewhere demanding your fealty, and assassins poisoning your food?

Lastly, I like that the alignment of the player character seems to influence who is drawn to the domain and for what purpose. The Good character's realm will be inhabited by Good people and threatened by Evil-doers, and vice versa. One realm is populated by dwarves and elves and fey, while the other is inhabited by manticores and orcs and ogres. I imagine that both types of domain are not entirely harmonious internally - I'm sure the dwarves and elves have beef and the fey play tricks on people, and the orcs and ogres contend with one another unless united by bribes and coercion from the local ruler.

This concept could be broadened beyond the realm of alignment only instead to the nature of the character in general. A dwarf's domain will attract more dwarves and an elf's domain will attract more elves. A paladin and a ranger will both rule Good domains, but their inhabitants will look very different, as will a cleric's and a druid's.

While I like the emphasis on player agency in the text, I don't much like the attitude that intervention on the DM's part is a last resort option. It doesn't make much sense to me that (if I'm reading this right), the Lawful Good neighbors of the player character's Chaotic Evil domain will only make some effort to overthrow the neighboring ruler if the player character takes the initiative first. If you're building a barony of ogres and mustering an army within your borders, the powers that be will take notice and intervene to the extent they are able.

The takeaway here is less that you should use specifically AD&D's system for any of this, but that you can take away certain broad ideas when including domains (whether player characters' or NPCs') in your campaign:

• Monsters move around the wilderness looking for places to live.
• Domain rulers have to contend with monsters wandering into their territory.
• Domain rulers can prevent monsters from wandering into their territory by placing warning signs, patrolling the surrounding area, and inducing settlers to inhabit it.
• Roads connect the domain to civilization as a whole, but introduce their own complications.
• Domains in the wilderness and those in inhabited areas have their own distinct complications.
• The character of the domain's ruler will influence who lives there and who opposes them, what their goals are, what problems they deal with, and the like.
• The inhabitants of the domain are somewhat an extension of the character to be used to raise funds and armies and achieve whatever it is the player desires. 
• Likewise, these inhabitants are a resource of the character which can be attacked much like anything else on the character sheet (in this case, they're almost like the domain's "equipment"). They are usually attacked by the domain's ideologically opposed enemies and neighbors.

That's my attempt to reckon with AD&D's domain game. While a lot of AD&D's actual mechanics often seem archaic or inscrutable, its broad ideas and procedures are often quite good. This is one of the few times where I find the procedure itself to be difficult to wrap my head around and borderline unusable, but once again the big ideas and overall feel of the system is solid, and there's a lot of good stuff to take away for whatever D&D-like game you may be playing.