# How exactly do cylinder spells and effects "ignore obstructions" in their areas? Or what kinds of obstructions they can realistically ignore?

So, Spell descriptions on Area entry says:

When casting a cylinder-shaped spell, you select the spell’s point of origin. This point is the center of a horizontal circle, and the spell shoots down from the circle, filling a cylinder. A cylinder-shaped spell ignores any obstructions within its area.

I feel like "any" is a bit to strong claim for how it does actually work.

Could someone elaborate step-by-step, how do you actually target such a spell when there are:

• a low wall in a spell's area;
• a wall, higher than the height of cylinder's point of origin, selected by a caster;
• ceiling above one of desireable "targets", but lower then a mentioned point of origin?

Should all of them really be ignored?

I think this is a poor description, because it is trying to describe a method of drawing a particular volume (by drawing a horizontal two-dimensional shape on the $$\XY\$$ plane and projecting it downward on the $$\Z\$$ axis), but then also using that as the description of what the spell itself is doing. The reason that’s a problem is because the combination of two factors here undercut any concept of the spell being “projected” at all. The first issue is that spells come into effect instantaneously; there is no time at which an effect is just the circle and then it travels downward. The other issue is the last quoted line, “A cylinder-shaped spell ignores any obstructions within its area,” which says we have to ignore anything blocking the projection on its way downward.

The sum of those two effects is that the spell isn’t “projected” at all, but simply comes into existence at all points within the volume simultaneously, without regard for what else is in that volume or where any point within is in relation to any other point in it. This is a valid way to imagine magic happening, of course, and probably appropriate for many spells. Moreover, even when it isn’t precisely appropriate, the top-down projection is very specific and definitely isn’t going to apply in a lot of cases, so it makes sense to avoid implementing that as a global default. All of which they could have easily just said, and relied on the “projection” description to talk solely about how you should draw the shape/know you have the right shape, but they didn’t do that. Instead, they talk about the “spell” doing that, and then need to apply the “hack” of having it ignore obstructions.

Anyway, yes, the long and short of it is, the official rule is that, by default, cylinder-shaped spells simply fill the entire volume without regard for what’s in it, or where any point is in relation to another or the existence of anything between them. Which is kind of nonsensical for some spells, but appropriate for others, so we should look to individual spell descriptions creating exceptions for those spells that actually want effects to come down from above. (Of course, I imagine, a great many authors of individual spells didn’t double-check the default rules and think through these concerns, and probably many spells that should have such an exception lack it—that’s where the DM comes in.)

• Could this include an example? That is, what exactly happens if a dude casts flame strike on an area in, like, a tent with a low ceiling? The spell's entry says Area: Cylinder (10-ft. radius, 40 ft. high), so if the tent's ceiling is only, like, 7 ft. does the full area get filled with flame, the area above the tent's ceiling, or the area below the tent's ceiling? Is the tent itself unharmed? Or is this it's own question? Sep 15, 2020 at 18:08
• @HeyICanChan The full volume is full of fire at all points, both above and below the tent’s canopy. The tent itself is certainly subjected to the effect as well, as appropriate for its hardness and other stats. The presence of the word “downward” in the spell’s description arguably makes a case for a DM to rule that it shouldn’t fill the entire volume, that this is a spell that actually is supposed to come down from the heavens rather than simply appear at all points simultaneously, but then that contradicts the official rule, which isn’t about appearing at all points but ignoring obstacles. Sep 15, 2020 at 18:37
• If the result is a damaged or destroyed tent, then is there any way for a reader to reach that conclusion naturally from the tex,t or were the rules just not completely thought through? (So like much of 3.5 when one starts drilling into it.) I mean, the tent hasn't been ignored by the flame strike effect if it's damaged or destroyed by the flame strike effect, right? Sep 15, 2020 at 18:48
• @HeyICanChan Ah, I see your angle here. I think, though, that one has to read “ignores any obstructions” as “ignores any obstructions for the purpose of determining where the spell’s area can reach,” that is, “ignores any obstructions as obstructions.” Not just ignoring them wholesale, for example as potential targets. Because if we don’t do that, then cylinder spells can’t affect anything at all—they have to ignore anything that might block their spread, which is to say, anything and everything inside them—and if that “ignoring” extends to affecting the target as well, then nothing is. Sep 15, 2020 at 19:11
• @HeyICanChan Absent the line about obstructions, I think it’s perfectly clear that flame strike would damage a tent—it’s something within the spell’s area that has hp and can be damaged, and flame strike is dealing damage. Nothing in its targeting or details suggests that its damage is limited to creatures or anything of the sort. It is unclear what happens if a spell destroys an object that would otherwise block its area, but thanks to cylinders ignoring any obstructions, that isn’t an issue for flame strike. Sep 15, 2020 at 19:13

The wording "A cylinder-shaped spell ignores any obstructions within its area" really is obscure - especially if we take into account that there has to be a line of effect from the spell's origin (which is the cylinder's top circle) to any square within the spell's area in order to affect them.

A burst, cone, cylinder, or emanation spell affects only an area, creatures, or objects to which it has line of effect from its origin (a spherical burst’s center point, a cone-shaped burst’s starting point, a cylinder’s circle, or an emanation’s point of origin).

A line of effect is a straight, unblocked path that indicates what an ability, effect, or spell can affect. A solid barrier cancels line of effect.

So the rules demand "a straight unblocked path" and at the same time say we should "ignore any obstructions".

A way to deal with this discrepancy would be to rule that cylindrical areas work similar to spreads which Skip Williams suggests in his rules of the game article on Reading Spell Descriptions (5).

Cylinder: A cylindrical area is something like a spread. The area extends from the point of origin in a horizontal circle, and then extends downward. The rules say a cylinder ignores obstructions in its area, which isn't too helpful. In effect, this means that line of effect for a cylinder isn't blocked so long as you can trace an unbroken line from the point of origin without leaving the confines of the cylinder. (You still need line of effect from you to spell's point of origin, however.)

• Rules of the game, as it often happens, not too helpful here. Two different places call "point of origin" two different things (upper circle's center and upper circle itself). Do you need lines of effect from upper circle's center to upper circle's other points before needing other lines of effect from those other points downwards? Or upper circle just happens no matter what may interfere with it, and you need lines of effect from it's points downwards? Or do you need lines of effect from upper circle's center to every point in cylinder's area? Sep 16, 2020 at 19:14
• @annoyingimp The Player‘s Handbook refers to "a cylinder’s circle“ as the spell‘s "origin“ (page 176). That‘s confusing because - like every area spell – a cylinder also has a "point of origin“ which is the center of the circle. I think, the rules of the game article provides a way to clear this up by saying that it‘s crucial to have an unbroken line from the point of origin without leaving the confines of the cylinder. Sep 17, 2020 at 8:51