The Manual: Designations

How to Get Here

Press d from the main view.

Description

Here you can designate areas for digging, detailing, plant gathering and wood cutting, among other things.
Use the displayed keys to select which type of activity you are designating.
Press ENTER to place one corner of the area you are designating. All designated areas are rectangles. Move the cursor and press ENTER again to finish the designation.
If your designated area has encompassed any appropriate map squares, they will become highlighted. Detail highlighting is not always visible, but you can view it whenever you are designated. Dig, chop and gather detailing is always visible.
Removing designations works in the same way as assigning them. Any highlighted designations that are encompassed by your rectangle will be removed. This includes any active jobs.

Mining

A few things to keep in mind: You must connect a down staircase to an upward staircase in the level below. If you select a floor as a channel, your dwarf will dig out the wall below as well. Regular mining leaves a floor layer betwen adjacent levels.

Smoothing/Engraving

Any rock wall or floor can be smoothed. Smoothing increases the value of rooms, which makes the dwarves happier and attracts more dwarves to your fortress. You can subsequently make engravings in the smooth surface to increase the value further.

Fortifications

Any detailed wall that is open on opposing sides (up/down or left/right) can be turned into a fortification. Fortifications have no monetary value, as opposed to normal detailed walls. However, dwarves can fire through fortifications. If you have dwarves equipped with crossbows, they can be positioned safely behind fortifications, which still act as walls.
In addition, units cannot fire through fortifications from a distance unless they make a skill roll, so you dwarves can fire safely through them even at enemy ranged units.

Forbid/Reclaim

Use these designations to stop a dwarf from using an item or to reclaim an item that has been forbidden. When you send an expedition to reclaim an old fortress, all of the items there will start out forbidden.

Constructions

You can remove constructions (such as wall and floor sections you've made from blocks) using the Remove Construction designations. You cannot mine or make engravings on these sections.

Traffic Designations

You can set traffic areas to bias the movement of your dwarves. Dwarves will prefer to walk through high traffic areas. Normal traffic areas are not displayed. A restricted traffic area does not prevent pathing, but dwarves will seldom use restricted areas if there is another way to get to their goal.

Slaves to Armok: God of Blood, Chapter II: Dwarf Fortress