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The Rules Compendium says, "The point of origin of a spell is always a grid intersection," then later says, "An emanation spell functions like a burst spell, except that the magic continues to radiate from the point of origin for the duration of the spell" (135 and link mine).

However, many area spells that are also emanations see their areas centered on the caster. For example, the ever-popular 6th-level Sor/Wiz spell antimagic field [abjur] (Player's Handbook 200) has the entry Area: 10-ft.-radius emanation, centered on you.

Does the caster of a spell that has an area entry of emanation centered on the caster pick a grid intersection adjacent to his space as the spell's point of origin? If so, then can a big caster sometimes see that emanation affect less than the space the caster occupies? Or does the caster of a spell that has an area entry of emanation centered on the caster count squares from the edges of his space into squares around the caster… in a manner that's largely contrary to the rest of the game and the description of area spells themselves? Or is there another option that I'm just not seeing?

If addressing examples makes an answer clearer, I'm particularly interested in what area is covered by the antimagic field spell's effect when the spell's cast by a Gargantuan creature (that has a space of 20 ft.) and if that big caster suffers (or doesn't suffer) the field's effect. I'm also interested in if a living Gargantuan caster of the 6th-level Clr spell antilife shell [abjur] (PH 199–200) sees that spell effect prevent living creatures from approaching only some—rather than all—of the caster's squares.


Note: I cite the Rules Compendium because it's often considered the last word on the rules, yet here seems to provides little guidance, essentially parroting the Player's Handbook on Area (175). Feel free to use either source. I've not tagged this question because I don't really need this lawyered but playable, but rules supporting opinions are, of course, preferred. Inspired finally to ask by this question, but this's been bugging me for ages.

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  • \$\begingroup\$ This may be related. NEB, if you use rulling similar to the one given in curent answer here, may be an actual burst and a centered on a caster one. And emanation spells function like burst spells. \$\endgroup\$ – annoying imp Mar 17 '18 at 19:46
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    \$\begingroup\$ @annoyingimp (The accepted answer is my answer that, in part, says, "In particular, emanations… would've benefited greatly from only a few more words of explanation and a diagram." Yes, this has been bothering me for three years! :-)) \$\endgroup\$ – Hey I Can Chan Mar 17 '18 at 19:59
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I would assume that, for emanations centered on the caster or another creature/object, you would actually calculate the area off of every grid intersection coming off the emanating creature's edge-most grid squares. My reasoning is more logic- than rules-related, but if a creature is emanating a effect in a 30' radius, and another creature is only 25' away from that creature, I would rule that the creature is affected. This accomplishes many things: it keeps spells even with simple 5' radii effective for larger creatures, it keeps the effect area circular based on the position of the emanating thing.

TLDR: we treat emanating creatures kind of like reach-with-given-radius in 360 degrees, but I've got nothing rules-wise to back that up. But it makes things always work smoothly.

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  • \$\begingroup\$ Since larger creature spaces are always square, you end up with an area that is more of a square with rounded corners than anything properly circular, even by the grid’s odd definition of a circle. Still, +1 for being what our group does, and the best answer I can think of, anyway. It does mean that creature space effectively increases the size of these kinds of emanations, but... I’m OK with that? \$\endgroup\$ – KRyan Mar 16 '18 at 16:09
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    \$\begingroup\$ RE: "[C]alculate the area off of every grid intersection coming off the emanating creature's edge-most grid squares." Wouldn't that see bigger areas creating weird pointy bits sticking off them, sort of like a 4-Venn diagram with 4 circles around a single intersection? \$\endgroup\$ – Hey I Can Chan Mar 16 '18 at 16:29
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    \$\begingroup\$ @HeyICanChan eh, just treat it like you would reach. 10' radius == 10' reach of spell. It just makes things go smoothly and it can be calculated quickly/easily. In the end, it lets the great wyrm dragon cast antimagic field on itself and it actually works. \$\endgroup\$ – Wannabe Warlock Mar 16 '18 at 16:45
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    \$\begingroup\$ @HeyICanChan That would be if you did it just from the corners, but if you did every grid intersection around the perimeter, it would “fill in” the gaps in the sides. \$\endgroup\$ – KRyan Mar 16 '18 at 18:28

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