Area
Some effects cover a defined area. Sometimes an effect’s description indicates a specially defined area, but usually an area falls into one of the categories discussed below. Regardless of the shape of the area, you select the point from which the effect originates, but otherwise you don’t control which creatures or objects are affected. The point of origin of an effect is always a grid intersection, meaning the point where four squares touch on a tactical battle map.
When determining whether a given creature is within the area of an effect, count out the distance from the point of origin in squares, just as you would do when moving a character or when determining the range for a ranged attack. The only difference is that instead of counting from the center of one square to the center of the next, you must count from intersection to intersection. You can count diagonally across a square, but keep in mind that every second diagonal counts as two squares of distance. If the far edge of a square is within the effect’s area, everything within that square is within the effect’s area. If the effect’s area touches only the near edge of a square, however, things within that square are unaffected by the effect.
Source
Core Rulebook pg. 268
Most effects with an area function as a burst, an emanation, or a spread. In each case, you select the effect’s point of origin and measure its area from that point. Source Core Rulebook pg. 268 |
Most effects with an area have a particular shape. Source Core Rulebook pg. 268 |
Some effects have areas that target creatures or objects within the specified area. Unlike for targeted effects (see Target on page 272), you do not get to select which creatures are affected; the effect affects all creatures or objects of some kind in the specified area. If an effect restricts which targets are affected (for example, it affects only living creatures), then creatures in the effect’s area that are not of the appropriate type do not count against the number of creatures affected. Source Core Rulebook pg. 268 |
If an effect targets creatures or objects directly, the result travels with the subjects for the effect’s duration. If an effect targets an area, it stays within that area for its duration; creatures become subject to the effect when they enter the area but are no longer subject to it when they leave. Source Core Rulebook pg. 269 |