I'm having some trouble understanding ramps.
For the purposes of unit movement, a ramp connects the ramp bottom to the tops of walls adjacent to the ramp bottom. So unlike stairs, where a dwarf moves directly up or down, a dwarf moving via a ramp will change both horizontal and vertical location in a single move. This can make it seem like a ramp has "direction" or "flow" by itself, but in fact this depends entirely on the spaces adjacent to the ramp.
More formally, for a creature to use a ramp, all of the following are necessary:
- The space directly above the ramp must be open.
- The ramp must have a wall next to it (including diagonals)
- The space above at least one of the adjacent walls must be open.
If these conditions are met, creatures will be able to move back and forth between the ramp space and the walkable space above the adjacent wall. Otherwise, the ramp will be labeled as "Unusable" when examined using the Look cursor.
Example A shows a situation where a ramp might be created that is actually unusable. Dwarves cannot ascend or descend (or cross) the ramp as shown because the walkable spaces above the ramp are not walled underneath, therefore dwarves cannot move between the ramp bottom and the spaces by the top of the ramp. If walls were added under the upper floor spaces, the ramp would become usable.
Note: Fortifications CAN be used by ramps as the adjacent 'wall', provided those fortifications have walkable space above them (which would apply to all carved out fortifications, or those constructed with additional flooring).
Finally, wagons follow a completely different set of movement rules on ramps. This can be exploited used to create separate paths for wagons and other (walking) creatures, for example to allow wagons to proceed directly to a depot while directing all other visitors through a trap filled maze.
This makes zero sense to me at all. i.e. there isn't a single part of the explanation that makes sense to me at all. What makes ramps usable in Dwarf Fortress?