But, doesn't Locate City target the city, not the people in it?
It's a rather unfortunately-worded spell. It doesn't actually target anything: it's an area effect spell that covers a circle (not a sphere) centered on the caster with radius of 10 miles per caster level, in addition to its range. This combines with splatbook metamagic for serious shenanigans:
1. Apply Snowcasting (
Frostburn, pg 50) to give it the Cold modifier.
2. With the Cold modifier, apply Flash Frost (
PHB2, pg 91) so that it now deals 2 damage to all creatures in the area of effect and makes the area slippery
3. Due to having an energy descriptor from Step 1, the application of Energy Substitution (Electricity) (
Complete Arcane, pg 79) now makes it deal Electricity damage.
4. The Born of Three Thunders (
Complete Arcane, pg 76) converts half of that Electricity damage to Sonic damage, but also allows creatures affected a reflex save, which allows the entire reason for this roundabout method...
5. Explosive Spell (
Complete Arcane, pg 79). The spell now shunts all creatures that fail their reflex save outside of the area of effect...in other words, it throws them tens of miles in a single round. Hilariously, Explosive Spell means that any creature moved this way takes 1d6 points of damage per 10
feet moved, and for those metric-folks, there are 5280 feet in a mile. Someone who moves one mile takes 528d6+1(Elec)+1(Sonic) damage. Someone who's right next to the caster will be a fine paste. If you hit something between your starting point and the edge of the spell, that's another 1d6 damage.
It is suggested that the caster tether themselves to something sturdy before casting in case they fail their own Reflex save.
Primary cuts against this are either to rule that the circle effect of Locate City doesn't actually follow the surface of the plane you're on (with the side effect that Locate City no longer locates cities), that you can't stack metamagic effects that way (lopping this off at Step 2, typically, since unfortunately Snowcasting explicitly allows Cold-based metamagic to be applied), that you can't apply damage to a spell that does not already cause some sort of damage (handily also cutting the caster off from dealing damage to the inhabitants of small countries), or more amusingly, to rule that it works precisely as written...only it simply punts everyone in range up an inch because a Locate Spell acts on a circle and not a sphere or cylinder, and the shortest distance to its edge of effect is thus along its nonexistent third dimension. A good way to give everyone in miles a kick in the rear and cause pratfalls, but not much else.
The counter to this last ruling was to replace steps 3-5 with Fell Drain (
Libris Mortis, pg 27): one negative level to all living foes that take damage from your spell. This causes every 1HD commoner in tens of miles that fails their saves to drop dead and, 24 hours later, revive as a wight. Since wights create more wights by killing more people, hilarity ensues.
EDIT: Added splatbook sources and the actual damage potential this bomb has. For the curious, Locate City is itself located in
Races of Destiny, pg 166, and is a Level
1 spell.
I think the OOTS are worried about being stuck with a bunch of negative levels when they encounter the very dangerous high-level vampire clerics who may have mind-controlled large numbers of very important Good dwarves?
That's personally my guess as well. Durkon and company will presumably be a difficult fight for them as they are right now. Stack on 3-6 negative levels per person on top of that, and the Order is going to be looking at a much nastier fight.