40d:Digging

Digging is a group of actions available from the designations menu. Digging is performed by dwarven miners in order to create empty spaces, hollow out material or dig stairs and ramps. All dig actions require a dwarf with the miner skill and an available pick.

Digging in 3D

The map is divided in layers. Tiles on each layer are composed by whatever is on that tile, and the floor (or absence
of floor) below it. A virgin rock tile is composed of a wall of rock and a floor of rock, for example. The ceiling of a tile is the same thing as the floor of the layer above that tile.

The most basic dig action is d mine. When this option is selected you can mark areas to be hollowed out from the current layer. Any useful material such as rock or ore is deposited on the ground excavated by the tile. Digging a tile preserves both the floor and the ceiling of that tile.

A similar action to dig is h channel. With this option it is possible to either select floor tiles (already dug out with dig) or 'full' tiles. When dug out, the floor (as well as a wall if it exists) on your layer will be removed and the tile on the layer below will be dug out. Creating a channel could be described as 'strip mining'.

Because it has the potential of removing two layers of wall and one of floor, channeling has the potential to be the fastest mining method. However, be careful that multiple miners working on the same channel don't undermine each other, causing them to fall through to the tile below. If this happens you may need to build a stair or a ramp in order for the fallen miner to escape.

Indiscriminate mining may cause Cave-ins.

Stairs & Ramps

For dwarves to move upwards and downwards between levels the construction of stairways and ramps is required. The most reliable way to assist your constructions is to dig an upward stairway on the lower level and downward stairway above. Stairs down only remove the floor, and Upward stairways do not affect the floor or the ceiling. Up/Down stairways act as a combination of both.

You can also construct these out of rocks or wood, but well placed dig commands are quicker. Digging downwards from the surface, first dig a j downward stairway. If you wait for this to be dug you will then see a visible block on the layer below where the stairway connects. In this tile dig an upward stairway. Your dwarves will now be able to access both levels using these stairs. It is advisable to build one of these before channeling in order for your dwarves to escape.

It may be convenient to build an i up/down stairway. This automatically creates a downward stairway on the floor above if you have not done so.^[Verify] This style creates an X symbol in place of a < on the default tileset, but leaves a > symbol on the floor above. You can also make a long series of up/down stairways directly above/below each other to make a long staircase that encompasses many levels.

Upward Ramps remove the ceiling above them and create a down-ramp automatically. They can't be used by dwarves unless built specifically. Up-ramps can be found in the same submenu of the designation menu as up- and down-staircases.

Ramps should be avoided until you need to provide access to caravans as dwarves on the upper level cannot perform actions such as dig, or build when standing on the ramp (imagine they are 'half way' up the ramp).

Stairs and Ramps can be removed using the z remove up stairs/ramps command, if those ramps were originally built by digging. Select this and mark the stairs/ramps to be dug out.

Dig Priority

Dwarves mine in veins: after mining a tile, a miner will pick the "next" tile (a tile that is adjacent to the one just mined). If there are several possible "next" tiles, the miner seems to pick randomly^[Verify]; this can break a large area into a large number of veins, which is inefficient.

To pick a vein (which is to say, a tile designated for some kind of dig job), dwarves seem to use a strategy similar to the one used for chopping trees or selecting plants to gather. Generally, they seem to pick the deepest, northwestern-most vein^[Verify]. Notably, dwarves do not pick the closest vein.

Dwarves have a priority over which side they will mine out from. Unless there is something in the way, miners will try to walk around unmined areas to reach these preferred sides, even if that path is very long. In order from most preferred to least preferred, dwarves prefer to stand on the tile to the:

West > East > North > South > NW > SW > NE > SE

of the tile being dug. If there is no path to the preferred tile (but the tile is safe to be on), the dwarf will cancel the job instead of standing on a less-preferred tile. This means that if the miner becomes stranded (i.e. after a cave-in or after digging a channel), the miner must find a way to be on the most-preferred tile to dig a wall back into the main fortress.

Because dwarves all use the same method to choose veins, dwarves tend to dig tiles near other dwarves. This makes having multiple dwarves dig together a bit problematic, as they will often get in each others' way.

Z-axis preferences untested, though it appears to me that dwarves prefer to dig out lower areas from a diagonally located area (i.e. not standing on the down stairs while digging out the up stairs directly below the down) ^[Verify].

These details are accurate for version 33g; they are likely to change in later versions.

Map Structure

If you are still confused about tunnels, floors and ceilings created by the mine command then look at the following diagram:

TOP VIEWS:      SIDE VIEW:
  LAYER 3       FROM -> 
  ██████..-     5 ██████
  ██████..-     4 ██████
->██████..-     3 ██████__
  ██████..-     2 ████  
  ██████..-     1 █████████
  
  LAYER 2
  ████████.
  ████████.
->████.....
  ████████. 
  ████████.
  
Key:
█ Solid rock
. Floor, visible from this layer
- Empty space, with a floor below
_ Ceiling (undermined section)

The Top Views try to show how digging into the mountain (on Layer 2) leaves a ceiling (floor) on the layer above. This is represented on the Side View by a thin line. Try to think of the mountain as a series of boxes where with a thin lid ontop of each. At any place the box can be filled or empty, and the lid above be there or not there. For example, you can create a wall and build a floor ontop of it. (Building a wall creates a floor on the next level by default, but this doesn't stop you building another floor construction ontop of it!)

Revised theory: Imagine the 3D world as a grid of boxes. Each box can have one of three states; Walled, Open space, Floor.

• Each cube can only be in one of these states.
• If a tile is Walled it is inaccessible, but the box above can be walked on (if an Open space or a Floor).
• If it is Open space, then it has no Floor and may be accessible.
• If a Floor is present, then the box is accessible.
• Additionally, floor constructions can be built in an Open space or a Floor box provided there is access from the side

--Markavian (Please discuss)

See also

• Map tiles - Different types of walled, floor and open spaces
• Mining - A description of the miner skill, used for digging