Suppose a wizard casts a lightning bolt due north (the origin is the upper left corner of his square and the line goes straight up along the grid). What squares does it affect?
If a line running along the edge of a square counts as going through the square, then this bolt should affect a path 10 feet wide and 120 feet long.
If the the edge doesn't count as the square, then the bolt affects an area zero feet wide and 120 feet long (that is, NO squares).
If the caster gets to choose a side, then the rules need to say so.
I realize that there are diagrams in the book, but those lack origin and end points and so are not very useful. They also don't match the words of the text.
SRD.
Umm, no.
A line-shaped spell shoots away from you in a line in the direction you designate. It starts from any corner of your square and extends to the limit of its range or until it strikes a barrier that blocks line of effect. A line-shaped spell affects all creatures in squares through which the line passes.
For the 30ft line,
Which corner of the square is the line starting from?What direction is it going (ie, where is the second point to determine the line)?
For the 60 ft line, why doesn't the line shown affect all squares through which the line passes?
The letter "C" narrows the origin down to one of four corners. To determine a line we need the specific corner and another point (like the end point) or some way to specify a direction. To determine which squares are affected, we also need to know whether traversing the edge of a square counts as going through the square and whether just hitting a corner does.
My belief is that the authors just cut and paste from the d20 SRD, which lacks the details presented in an image sidebar of the PHB. That text, or something similar, needs to be paraphrased in the Pathfinder rules and the diagrams need to be corrected so that they no longer contradict the written text.
for reference, here's the PHB sidebar:
A line describes some kinds of attacks (usually magical). It affects creatures or characters in a astraight line away form the spell caster's square to any intersection within range. All squares through which the line passes or touches are affected by the attack. The line continues to its full range, usually beyond the target intersection and possibly affecting more characters or creatures.
Notice how a target intersection is specified. Also notice how "touching" a square is clearly specified as sufficient to affect it (so passing through an edge or corner counts). If you have a PHB handy, you'll also notice that the picture accompanying the text on page 176 matches what is written and that the caster, origin, and target intersection are all shown.
I play Pathfinder exclusively for my d20-ish fantasy fix. I love it, but it's not perfect (yet).
If the c in the box designates the caster the spells originate from the top left most corner of the spell casters box. In the first example (the straight line) the spell is projected outwards to the top left hand corner of a box 30 feet away and straight ahead. It clearly only effects a 5 ft area.
In the second example the spell originates from the same source but is now traveling to the top right corner of the box immediately to the right of the caster.
It might help you visualize this better if you take a straight edge and bring it from corner to corner. In general the boxes that the straight edge passes through are those that are effected by the spell.
We just had this out with our group, thankfully i was the GM :)
Pass through in my mind means it passes through 2 edges of the square, these can be adjacent edges.
In the case of this, you would hit nothing as you would not cross 2 edges of the target square.
Looking at the diagrams is all well and good for those specific lines, but there are thousands of lines that can be made as the distance on line spells inreases, so its important to make a ruling on 'through' a square to deal with these also.
Suppose a wizard casts a lightning bolt due north (the origin is the upper left corner of his square and the line goes straight up along the grid). What squares does it affect?
SKR: "Running a line along the edge of a square isn't passing through that square, else the north-south diagram would be two squares wide and the southwest-northeast diagram would have extra squares (every square that's connected to the four-square intersections along the diagonal path of the line)."
I realize that there are diagrams in the book, but those lack origin and end points and so are not very useful. They also don't match the words of the text.
SKR: "My suggestion: Take a deep breath, calm down, and use the diagrams, they're clearer than the text, and better show the intent of how they're supposed to work."
Also note that this is a clear change from 3.5, where touching the edge of a square did count.
Grick, the diagrams do not cover all possibilities.
For example, 120 foot line spell, and you want it to hit a square 105 feet away, and 15 feet to the right.
Where does the line break? Can you tell me? I know i cant. This is where a piece of string works wonders.