DMG Appendix A

In the last post, I made some analysis of Gygax's Dungeon Geomorphs product. I've also been playing around recently with AD&D DMG Appendix A: Random Dungeon Generation. Let's use the insights to the former product to fill in some of the hidden assumptions in the latter. When using Appendix A, I would highlight or recommend the following:
  1. To start with, you should normally begin by going directly to a random room on Table V. (The "Start Areas" on p. 169 are visually arresting, but that's actually a secondary, optional start possibility. You don't want to re-use those a lot.)
  2. The tables probably generate more 45-degree passages and 20'-wide corridors than Gygax himself would actually use by default. Be ready to ignore or override those results a lot if they don't fit well into your map; in particular, I make all 45-degree passages automatically 10' wide (ignoring the fact -- as Gygax did -- that running along vertices on the graph paper, they're really just 7' wide).
  3. Rooms and Chambers (square/rectangular) should, for convenience, always be set up on the cardinal axes -- if accessed off a 45-degree passage, you should probably automatically make them Triangular or Trapezoidal. In addition, all Triangular/Trapezoidal rooms may as well be right-angled, setting them along the grid axes, and giving them a single 45-degree diagonal wall. Any side passage or "door ahead" in a 45-degree corridor should be set along a cardinal-direction, unless it explicitly states the angle at which it should be.
  4. By default, Rooms should have Doors, and Chambers should have Passages (i.e., non-door openings) as exits. This isn't explicitly stated anywhere, but it's implied in places like Table I (corridors empty into chambers but never rooms), Table II (doors open to rooms 4 times more often than chambers), and Table V-C (result of 19-20 indicates exceptional case of "door in chamber, passage in room").
  5. Note that the treasure containment tables (Tables V-H through V-J) are copied verbatim from the earlier Monster & Treasure Assortment product. Tables V-I and V-J (guarded by/hidden in) stand out in Appendix A because they don't have any game statistics associated with the entries. Particularly for solo play, I recommend ignoring these tables (per the "if desired" note -- contrast to Table VII: Trick/Trap, etc.)
  6. Also, when making Rooms/Chambers for solo play, I change the generation order to (i) Room shape/size on Table V, (ii) Contents on Table V-F, and last (iii) Exits on Table V-C, etc. This lets any fight be played out before consideration of egress, which cognitively feels better to me (e.g., see the recent discussion on when room size/detail description is appropriate).
  7. Note the somewhat unusual secret-door detection rates (by d20) on Table VII, result 1-5. I use this for all indicated secret door checks in Appendix A.
  8. Finally, I delete the entry on Table III for "passage X's", since I don't like how it treats cardinal-versus-diagonal passages asymmetrically (i.e., biased towards yet more diagonal passages).
Item (3) seems particularly important to me. When using Appendix A in the past, I would tend to get into a diagonal corridor (e.g., Table III actually generates more 45-degree side passages than 90-degree ones), and from that point on I'd be struggling to draw a whole connected region of rectangular rooms, chambers, and passages all diagonal to the graph paper. If you think about it, that really abandons all the advantages to drawing on graph paper in the first place.

If we instead re-set to the cardinal grid every time we enter a room or chamber, then we get more limited diagonal elements, less frustration for DM & players alike, and a dungeon much more like the designs Gygax had in mind when he was laying out maps such as those in the Dungeon Geomorphs and other products.


  1. Point 4 is directly supported by the Dungeon! boardgame, where chambers have no doors and rooms are only accessed via door.

  2. Delta---

    Out of curiosity, do you plan to do some analysis on early dungeon level maps too---whether from Castle Greyhawk or from G1 or the Greater Caverns map from S4 (the earliest published maps by Gary and Rob), to see how your assumptions about the geomorphs and random dungeon generation compare to them?


  3. Good point, Jeff.

    Allan -- I wasn't really planning any more than this; the intent here was mostly to develop some interpretations for DMG Appendix A.

    Seems like the original Greyhawk stuff we can peek at looks in the same general sensibility as Geomorphs/Appendix A. The fact that G1/S4 have cave systems (or above-ground structure for G1 1st level) changes the game a lot, compounding any philosophical change at that time.

  4. Couldn't help but notice a couple mentions there to "solo play". Are you talking about doing the generation solo, or are you actually using the random generator as some kind of DM replacement? I don't have my DMG here, so I'm not sure if solo play is something it specifically mentions as a use case.

    Either way, I'm curious how you find the experience. I've played plenty of T&T solo adventures, and made a point of collecting all the solo modules (Ghost of Lion Castle, Blizzard Pass, etc.) None are quite as satisfying as I'd hoped, but I haven't played through them all yet. Anyway, just curious what your thoughts on solo play at large are.

  5. Yeah, at the end it actually does specifically mention solo play, and recently I did start playing with it myself, sort of (a) filling some extra free time I have, (b) filling in for a video game, (c) acting as a playtest of OD&D balance all at once.

    I kind of have a lot of taste for open ended dungeon-crawl stuff, so combined as a science experiment to find & tweak rules that smell bad to me, it's not terrible recreation.

    "The random dungeon generation system is easily adaptable to solitary play. Locate the entrance to the dungeon, and then select one of the random dungeon starting areas given here, locating it in the middle of the graph paper." [AD&D DMG p. 173]

    This is followed by short paragraphs on (1) getting "special" designed areas from a friend, (2) adjudicating listen-at-doors, and (3) other ESP/detection devices.

  6. I am tickled that part of the rules for solo play involve getting a friend. :)

    I just picked up a copy of XS2: Thunderdelve Mountain at the GenCon auction and hope to spin through it soon. To date my favorite solo module was BSOLO: Ghost of Lion Castle. Though it kicked my ass repeatedly, it made for a much more enjoyable sick day than watching daytime TV.

  7. A late follow-up to the "Rooms have Doors, and Chambers have Passages (i.e., non-door openings)" dictum:

    That's also how it works in the Dungeon board game rules. Anything behind a door is a "Room", while the areas with no doors leading inward are called "Large Chambers".

    1. ... Which is the very first thing that Jeff Rients posted above, and somehow I overlooked his post 2 years later when the same thing occurred to me.