(Unofficial) FAQ of the GURPS Fora

[vicky_molokh]

On arcs of vision, Front, Side and Back hexes etc.
Not sure how frequently people actually get confused by this one, but this is probably worth keeping archived in the uFAQ:
Here is how these hexes are defined.

Originally Posted by Kromm

In general, the diagram on p. B74 or p. B389 should be used. The white hexes are where you have unpenalized defense, ranged attack, and Vision rolls; the gray ones are where you have penalties for the side; and the black ones are where you cannot attempt the task at all. This is a question of awareness . . . and note that for defenses, the question isn't "Can I reach this hex with a melee attack?" but "Can I defend against attacks coming out of this hex?" You can parry or block attacks from foes you can't easily attack.

Melee attacks (only) use the diagram on p. B388. This is more restrictive. The Front, 2, and 3 hexes count as "front" if you can reach them; the black hexes on p. B74 or p. B389 still count as "back"; and everything else counts as "side" and demands a Wild Swing.

The two differ mostly because it's easier to turn a head to see something, and possibly to shift a shield or weapon slightly to intercept something, than to launch a full-powered thrust or swing at it. That's a function of body dynamics. Missiles get a special pass and use the better arc because you just have to let go of the bowstring, pull the trigger, etc.; you do not have to follow through with all your weight and might.

An illustration courtesy of Brian Ronnle:
Example A is for Mêlée Attacks (remember that Jets count as mêlée!).
Example B is for vision, ranged attacks, and Active Defences, and probably everything else.