From the SJ Games website:
"In fantasy tales, cities can be safe havens, goals of quests, or places to visit along the way. Indeed, magical metropolises have served as settings for entire fantasy campaigns, where the heroes can find arcane adventure by going out their own front doors. When it comes to creating fantastic cities, you don't need an eldritch tome crackling with power; you only need GURPS Thaumatology: Urban Magics.
Building on ideas from GURPS Fantasy and taking full advantage of the possibilities opened by GURPS Thaumatology, this volume explores the distinctive nature of urban magic – how magical groups are organized, what magical practices a city supports, how cities make magic more effective, and how magic makes cities work better. In addition, it looks at the gods, spirits, and monsters that live in cities. All of these come complete with new GURPS rules and options. This supplement also includes:
Almost a dozen new templates with varied magical abilities, including suggestions for making them more or less powerful.
Five types of magic specific to cities: Tap the power of sacred architecture, urban divination, or ley lines.
How to make a city work using the GURPS magic system. Lights, water, power, and sewage – there's nothing magic can't handle!
Eight thematic campaign ideas that keep the action city-centric. Patrol the gritty streets as enchanted investigators, enroll in a magical school, or scheme in mystic mansions.
Whether organizing a mages' guild, tapping a city's unique essence, bargaining with the gods, or designing a magical city-based campaign, GURPS Thaumatology: Urban Magics has what you need!