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Area of Effect

Single target or single blast?

Odd thing, but as I'm vetting the Chimera 2.1 update, I started questioning area-of-effect (AoE) attacks. In my experience, the conventional wisdom for AoE has always stated that all targets within the blast radius take damage. Pretty straight forward, and you may be asking what could possibly be unclear about that.

Well, it's this: does area-of-effect damage apply to each target in a blast radius, or each occupied space in the blast radius?

This is an esoteric distinction, one that only manifests when you use miniatures on a gridded battlemat. But since that's a pretty common convention, I strongly suspect this has been debated before. Only, I don't know who won, and I couldn't find anything in my three-and-a-half-minute search of the Interwebs. Consequently, I'm opening up the issue for a fresh evaluation. While I have my own thoughts on the matter (of course you do, I hear you saying to yourself), I want to hear others weigh in on the topic.

Area of Effect Basics

Blast example #2 ('bots)

Area of Effect - 2 targets

Let's start with a gridded battlemat. The scale doesn't really matter—just assume that each square on the grid contains no more than one combatant. Some combatants, like dragons or horses or tanks, are big enough to take up more space—let's say two squares or more. Let's also introduce a straight-forward area-of-effect weapon, a grenade that does 1d6 points of damage with a blast radius of 1 square. This means that the blast radius includes about nine squares on the battlemat—the target square (ground zero) plus one additional square in every direction. When the grenade goes off, anything in one of those nine squares gets hit for 1d6 points.

This is shown in the illustration above-right. The red square is ground zero and the red circle is the area-of-effect. There are two Defence Robots within the grenade's blast radius, so each takes 1d6 points of damage.

Blast example #1 (tank)

Area of Effect - 1 target

Similarly, the second illustration (at right) shows a tank caught in the grenade's blast radius. Again, the red square is ground zero and the red circle marks the total area-of-effect. Note that the tank takes up two squares. However, it's still inside the blast radius (or, more accurately, part of it occupies the area-of-effect), so it also takes 1d6 points of damage.

These examples are straight-forward. In the first, you have multiple targets damaged because each occupies a square inside the blast radius. In the second, you have a single target that's damaged because it, too, occupies a square inside the blast radius. Simple.

But now I'm about to blow your mind.

Single Target or Single Blast?

What if a single target takes up multiple squares inside the blast radius? Does it take one die of damage because it's a single target, or does it take one die of damage for each square within a single blast radius?

Consider the examples above. When the robots are damaged, it's because each is within the blast radius. Same with the tank—it's also within the blast radius. The implication in both examples is that damage applies to each square within the area-of-effect. As a result, each robot gets 1d6 points of damage, as does the tank.

Blast example #3 (tank)

Area of Effect - large target

But what if the whole tank was inside the blast radius? As in, both squares occupied by the tank are inside the grenade's area-of-effect?

This is shown at right. As before, the red square is ground zero and the red circle is the blast radius. But this time, the entire tank is in the blast radius. So the question is, when it's hit by the grenade, does it take 1d6 (single target) or 2d6 (single blast) points of damage? Here are the approaches I've come up with:

Single Target Argument

  • Mechanic: Each target within the area-of-effect takes damage from the attack
  • Interpretation: If a target, or part of a target, is within the area-of-effect, it takes one die of damage
  • Rationale: Big targets resist damage better than small ones; plus, the damaged part of a large target may shield other parts from the blast

Single Blast Argument

  • Mechanic: Each square within the area-of-effect is subject to attack damage
  • Interpretation: A target takes one die of damage for each square it occupies within the blast radius
  • Rationale: Big targets risk greater exposure to the blast; plus, this is consistent with the apply-damage-to-each-square approach you'd use for smaller targets (like the robots, above)

And the Verdict Is...

I can appreciate the rationale for each approach, though the voice in my head keeps pitching the Single Blast Argument. After all, if there were a Defence Robot in each of the blast radius' nine squares, each robot would take damage, and that suggests that damage is applied to every square in the area-of-effect. That's a strong precedent against the single-target stance.

But, given a sufficiently logical and well-articulated appeal, I'm willing to be swayed. Broadly speaking, I have only two requirements: (1) whichever approach is used, it has to work in all situations—the last thing I want is a conditional mechanic for what should be a straight-forward ruling, and (2) the approach can't bog down play, and that includes taking time-outs to provide a lengthy explanation of why the approach I chose was chosen (that said, I'm all for providing short explanations that deliver iron clad justification in two sentences or less to keep the game moving).

So...what's your take? Do either of these arguments pass the sniff test better than the other? How do/would you handle this issue in your game? Is there a third mystery option my enfeebled brain has overlooked? Do you think grenades could even scratch a Defence 'bot?

Let me know. When I reach a decision—based on your input—I'll post a follow-up and put it in the Chimera 2.1 revision that's due out in a few weeks.

Battlemaps constructed in Fractal Mapper 8, using images from the CSUAC.

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  1. Syrsuro
    March 26th, 2010 at 04:12 | #1

    I would say the answer hinges upon one factor: is the ability to absorb damage/ the damage required to incapacitate the target proportional to the size of the target or not.

    Imagine two (mini)tanks, each taking one square compared to a single tank that takes two squares.

    If the larger tank was able to absorb twice (or more) of the damage, than making the effectiveness of area of effect attacks increase proportionally to the size as well would make sense. But if the ability to absorb damage is not related to the size, then you end up making large targets disproportionatly vulnerable to area blasts.


  2. March 26th, 2010 at 06:54 | #2

    @Syrsuro : Right. I see what you’re saying. In most cases, a 2-square tank might have greater resistance to damage than a mini, 1-square tank. But not always…

  3. March 27th, 2010 at 21:33 | #3

    UPDATE – 27 Mar 2010
    I posed the question to Jeff (yes, that Jeff), who replied sent the following email (permission to quote given):

    For me this comes down to the question: What if I don’t have minis and a grid out? Under these circumstances I just have to make best guesses about who is hit with an area of effect and who isn’t. With Single Target all I have to do is figure out who is caught in the blast. With Single Blast I have to figure out how much each target is in the blast radius as well. That introduces an extra step that I don’t particularly want to deal with. So based upon the purely practical consideration of not letting the rules bog me down in play I vote for Single Target.

    While I noted that this issue really only comes up when using figures, Jeff intimates a good point: you want a rule that will apply in all situations, minis or not.

    The pendulum is swinging the other way…

  4. deimos3428
    March 29th, 2010 at 14:37 | #4

    I’m going to cheat a bit in my response, as it is conditional — but it won’t bog down play as you only need to think about it before play starts. I believe it depends on the type of game you’re playing, and the decision needs to be made on a per-game basis.

    The Single Blast Argument works best in a tactical game, particularly one with fixed damage. In that case things like surface area and facing become more important. (Consider a donut-shaped alien mothership…it really should take more damage.)

    The Single Target Argument is a more reasonable abstraction for a non-tactical game with variable damage dice where you generally just want something fast and loose. As you noted, there is a “ground zero” which could be used to handle this seeming disparity — at least in part. In the second example, the tank is within the ground zero and might perhaps take double damage.

  5. March 29th, 2010 at 16:27 | #5

    My vote would be for Single Target, because it’s simpler (as illustrated by jrients). Look, the whole concept of a defined Area of Effect is a gamey abstraction to make the rules easier to read and apply. Post-combat analysis has revealed dozens of cases where a soldier has a grenade or mortar round go off almost at his feet and survived relatively unscathed, while another was killed or severely wounded by flying shrapnel despite being 100m away from ground zero. Every explosion is different, a chaotic system in miniature, but we make them deterministic in-game to keep play flowing (a more “realistic” ruleset would have random processes for determining the size, shape, overpressure intensity, shrapnel density, etc. for each grenade thrown). Since we’re abstracting so hard anyway, make the simpler choice. That said, it’s not a deal-breaker either way you go. Keep up the good work…I’m looking fwd to downloading Chimera 2.1!

  6. March 29th, 2010 at 20:09 | #6

    @deimos3428 : Good distinction, Deimos. If the game were all about minis and a battlemat, it would be easier. I hear the point about ground zero, too–in the 2.1 upgrade, targets in the blast radius get a DEX check for half-damage, except for the poor sod at ground zero.

    @Rich Spainhour : Thanks for making me take another sip of my own Kool Aid. Chimera is all about abstractions, so why complexify this?

    Thanks for the feedback, guys. Single Target it is!

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