From Compendium of Worldly Lore
Needs review
Source: Cityscape
Description: You can use the city itself to enhance your spellcasting.
Prerequisites: 3rd Level Caster
You can modify any damaging spell you cast to incorporate the urban environment, when casting an offensive spell with an energy subtype - Acid, Cold, Electricity, Fire, or Sonic - you can invest the spell with a portion of the city's spirit. In most cases this investment is gritty and spectacular, drawing dirt, gravel, nails, and other nearby detritus into the spells effect. In other cases, the investiture is much more subtle, often merely changing the look of a spell. Only half the damage from a spell of the appropriate subtype is considered energy damage, and is thus subject to resistances or immunities, the remainder comes from the city itself, and is not subject to resistances or immunities. This investiture only occurs for spells cast within urban environments, defined as any area above the size of a small town.
For example, a wizard uses City Magic to cast a fireball at a creature with resistances to fire 15, the damage roll is 20, half of it fire damage, and half 'City'. Thus, the target takes 10 points of city damage instead of 5 damage fire damage. This feat is useless to casters who cast their spell in a non-urban environment as defined above.
A spell modified using city magic feat uses a spell of the spells normal level.