Level type

For the standard, randomly-generated, level, there is a certain level type associated with it.

For dlevel < 3, the level type is always normal.

For dlevel < 6, the level type is 7/12 normal, 2/12 small rooms, 1/12 warehouse, 1/12 city, 1/12 caves.

For higher dlevel, the level type is 2/11 normal, 2/11 small rooms, 2/11 warehouse, 2/11 city, 2/11 caves, 1/11 maze.

Caves are replaced 1/4 of the time by arenas.

There is another level type that is in the code but doesn't spawn in 0.9.9.3: For dlevel > 15, there is a 1/25 chance of any type being replaced by the mysterious and deadly single monster type level. This will probably be truly added in 0.9.9.4.

Arena

The arena is a very basic map type. There are no walls, save those that create the map border, and you spawn right in the middle of a huge room with nowhere to hide. Enemies tend to specifically hunt you on these maps, and there are four sets of stairs lodged in the very corners of the level.

There are four possible configurations for the walls around the player depending on a roll of 1d25 + max(dlevel, 25).

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The following statistics are associated with the Arena level type:

Monster Placement

The total danger rating is only 67% of the normal value to accommodate the increased difficulty. In addition, every monster has a 50% chance of being placed in hunting mode at the start of the level. Monsters in hunting mode will seek out the player even if they can't see him.

Item Placement

Arena type levels always drop 10 items.

Room Placement

There are no randomly-generated rooms in arenas.

River Placement

Arena levels never generate rivers.

Fluid Placement

The fluid generation stage is repeated 3 times. As a result, much more fluid is generated, helping to make up for the lack of walls.

Cave

Caves are much like arenas, although their wall composition is far more natural-seeming with plenty of spindly paths hidden in the edges. They are, bar none, the most infamous map type due to their very limited spawning pool of enemies, the later of which are very difficult to fight without cover (and cover in caves is sparse to say the least).

The following statistics are associated with the Cave level type:

Monster Placement

The total danger rating is only 67% of the normal value to accommodate the increased difficulty.

Cave type levels only include a single monster type. The monster type is determined by a roll of 1d5 + dlevel + 3 × (difficulty - 2) - 3. (Difficulty is 1 for itytd, 2 for hntr, etc.) Usually the monster type is as follows:

If the roll is at least 20 and the difficulty level is Ultra-Violence or Nightmare!, there is a 1/5 chance of a pain elemental cave instead of an arachnotron cave.

For rolls of at least 50, the cave will instead feature a nightmare enemy: nightmare demons, nightmare arachnotrons, and nightmare cacodemons are equally likely.

For rolls of at least 81 on Ultra-Violence and Nightmare!, there is a 1/5 chance of a lava elemental cave instead.

The amount of monsters is as normal, except only the chosen monster type can be placed. Also, the total danger rating for the level is only 67% of the normal value.

Item Placement

Cave type levels always drop 10 items.

Room Placement

There are no randomly-generated rooms in caves.

River Placement

Cave levels have a 1/3 chance of generating rivers. Horizontal rivers are chosen 1/3 of the time and vertical rivers are chosen 2/3 of the time. Cave levels can only have a single vertical river. To help ensure the river is connected to the rest of the level, the starting x coordinate has a reduced range of 1d16 + 33.

Fluid Placement

For caves, the fluid generation is closely related with the level generation is a whole. In particular, a cave type level is almost guaranteed to have some fluid, and the fluid type respects the same ranges as above.

City

A few, small rooms inside a huge "city". Luckily you don't tend to get ambushed as much in cities, you just have a few roaming monsters and others staying put inside their little rooms.

City type layouts are characterized by an empty map with scattered rooms. The rooms in a city level have x-dimension between 6 and 15 and y-dimension between 5 and 11 (including the walls). Each room has exactly one door. The door is equally likely to be on any wall tile (but never on a corner). Rooms always have a 1 tile buffer on all sides where no other rooms can be generated. There are always at least 2 tiles between the walls of a room and the outer walls of a level.

The following statistics are associated with the City level type:

Monster Placement

There is no change in monster placement from the standard model (see link in title).

Item Placement

Items in City type levels are based on the normal calculations (see link in title).

Room Placement

The expected number of rooms generated is hard to calculate exactly, so here are some (expected) room generation parameters that were collected on a sample of 10000 random city layouts:

River Placement

City levels have a 1/3 chance of generating rivers, but cannot generate horizontal rivers. Rivers are generated before the layout is generated; as a result, the rooms will never overlap with the rivers, and levels with rivers will tend to have fewer rooms.

Fluid Placement

The fluid generation is typical of how fluids are normally calculated (see link in title).

Maze

Mazes are annoyingly hard to traverse. They have no doors and rarely open areas (which are usually caused by fluids). Because of the perpetual situation of being in close quarters, it is easy to hide from monsters around corners but also easy to be caught by surprise or trapped. Be aware when you hear monsters: they are probably tracking you and may emerge without warning around a corner.

The following statistics are associated with the Maze level type:

Monster Placement

Maze type levels have a 50% increased total danger rating.

Item Placement

Maze type levels always drop 1d8+10 items.

Room Placement

There are no randomly-generated rooms in mazes.

River Placement

Maze levels have a 2/3 chance of generating rivers. Horizontal rivers are allowed.

Fluid Placement

The fluid generation is typical of how fluids are normally calculated (see link in title).

Normal

The classic map. The whole screen split in to rectangles divided by rooms. Early on they are very common (100% guaranteed for your second map, in fact) but tend to fade out in favor of other map types.

Normal type layouts divide the map into rooms. At each step, a coordinate is picked, a door is placed in that position, and then a wall (either vertical or horizontal) is extended in both directions until reaching a wall. 10 walls are placed in total. Vertical walls always start from positions with even coordinates and horizontal walls always start from positions with odd coordinates. (The upper-left corner which is always a wall is (1, 1))

The first two walls are always vertical. One starts at a (even) point in the range (4, 4) - (36, 18). The other is in the range (38, 4) - (70, 18). (ie one is on the left side and one is on the right side.)

For the rest of the walls, vertical walls will start at even points in the range (4, 4) - (76, 14) and horizontal walls will start at odd points in the range (3, 3) - (75, 17).

The next three walls are always horizontal. Each of the last five walls has a 1/3 chance to be horizontal and a 2/3 chance to be vertical.

If the point chosen at any step is already a wall, then only the door will be placed. For this reason there are sometimes fewer than 11 rooms in the final map.

The following statistics are associated with the Normal level type:

Monster Placement

There is no change in monster placement from the standard model (see link in title).

Item Placement

Items in Normal type levels are based on the normal calculations (see link in title).

Room Placement

The expected number of rooms generated is hard to calculate exactly, so here are some (expected) room generation parameters that were collected on a sample of 10000 random normal layouts:

River Placement

On normal type levels, either rivers or normal fluids are allowed, but not both. There is a 50% chance of each. Horizontal rivers are allowed.

Fluid Placement

The fluid generation is typical of how fluids are normally calculated (see link in title) other than that, if a river is generated, then no other fluids are.

Small Rooms

Also known as "archi", a small rooms floor is a claustrophobic's nightmare. Lots of little areas connected by doors, and very easy to get caught if you're not careful. Whereas caves and arenas cause trouble because the enemies swarm effectively, small rooms make explosive and powerful enemies that much more dangerous, as there's no easy means of escape. Fortunately, due to the current movement of the AI, the enemies tend to stay in the center of the map, making the outer rooms fairly safe.

The layout is generated by dividing the map into a 4 by 3 grid of equally sized sections. Each section is given one of the following 12 sublayouts uniformly at random (repeats are allowed):

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These sublayouts are placed so that their walls overlap. Doors that would lead to the edge of the map are removed.

The following statistics are associated with the Small Rooms level type:

Monster Placement

There is no change in monster placement from the standard model (see link in title).

Item Placement

Items in Small Rooms type levels are based on the normal calculations (see link in title).

Room Placement

Despite the name, levels of this type to not generate special room features.

River Placement

Small room type levels have a 1/4 chance of generating rivers. Horizontal rivers are allowed.

Fluid Placement

The fluid generation is typical of how fluids are normally calculated (see link in title).

Warehouse

The warehouse map is very plain but can be very tricky to handle. Three rooms containing "boxes" (although these are indestructible: compare to warehouse rooms) with slightly random spacing between them. These levels can be considered more "pillar" maps than anything.

The following statistics are associated with the Warehouse level type:

Monster Placement

There is no change in monster placement from the standard model (see link in title).

Item Placement

Items in Warehouse levels are based on the normal calculations (see link in title).

Room Placement

There are no randomly-generated rooms in warehouses.

River Placement

Warehouse levels generate rivers 1/6 of the time, but never at the same time as normal fluids. Horizontal rivers are allowed.

Fluid Placement

The fluid generation is typical of how fluids are normally calculated (see link in title) other than that, if a river is generated, then no other fluids are.

Single Monster

This level is similar to the Normal type map, except that all monsters are a single monster type.

The following statistics are associated with the Single Monster level type:

Monster Placement

Single monster type levels choose monster types based on a roll of 1d10 + min(dlevel + 3 × (difficulty - 2) - 4, 20). The amount of monsters is indicated as a fraction of the level's usual total danger rating (100% if not noted). The level feeling depends on the monster types.

For rolls of 26-27, there are two possible levels: pure arch-viles which happens 2/3 of the time and arch-viles mixed with formers with happens 1/3 of the time. For rolls of 28-30, the result is usually the former human level (same as roll < 17), but if dlevel > 50 and the difficulty is Ultra-Violence or Nightmare!, then there is a chance of a harder monster type.

Item Placement

Single monster type levels generate 50% more items (rounded down).

Room Placement

There are no randomly-generated rooms in single monster levels (to our knowledge).

River Placement

There are no rivers in single monster levels (to our knowledge).

Fluid Placement

The fluid generation is typical of how fluids are normally calculated (see link in title), to our knowledge.