I think as often as my books begin with a character or an idea, they begin with a place.
Sometimes it’s an epic place, like the Chimayo Badlands in New Mexico:
Sometimes it’s an amazing place, like San Francisco, California:
And sometimes it’s a familiar place, like the historic building where my husband works:
All three of these places have inspired stories, served as places where my characters can live and laugh and love. While other people may see, well, a desert and a city and a shopping mall, I see a cursed land and a world of magic and a gamer’s playground. These places, which have, at different times of my life, been my home, now belong to me as much as I ever belonged to them.
It’s not a one-for-one exchange, though. I pick and choose what parts of the place will appear in my fiction, and I corrupt them, changing them in big ways or small, while the effect they’ve had on me is permanent and complete. I will never be the same, for my time in San Francisco, while the city itself is untouched by my fictionalizing influence.
When I wrote SHAKEN, I wanted to make magic a physical part of the landscape. That gave me an excuse to play with the city’s historical quirk: my San Francisco never voted to stop burying the dead within city limits, and the remains of the dead are magically important to the city’s atmosphere.
Hmm. It sounds creepy when I put it that way.
Magical pollution by the dead aside, the fact remains that my San Francisco means nothing to the city itself, and has changed nothing for anyone living there. It’s my city now, and has less to do with the actual city than that city has to do with my creative influences. Landscapes alter our dreamscapes, and that in turns shape the way we write our stories.
Where do your stories live?
Spellbound Scribes 
I love this! Most of my stories begin with a setting too. And when I wrote an UF set in London, I felt the same way you did about San Francisco–the city in my imagination was indelibly altered, even though it stayed the same in real life. But the cities we inhabit in our fantasies can seem just as real as their real-world counterparts!