In To Play the Fool, the setting is generally San Francisco, and the time period is generally the early 1990's (hence the minimal mention of doing research on line, and with a modem!)
Saying "it happened in San Francisco" is a bit like saying "it happened in Canada". You can draw some general conclusions about some things. But just as Canada is a lovely and terribly diverse and exciting country, the San Francisco area is amazingly diverse.
Here are some of the areas that King visits in the novel:
Russian Hill (Kate and Lee's home): In the first book in the series, we found out that Lee inherited the house from her mother. Kate and Lee have been working on renovating the old house since they moved in. You can read some histories of Russian Hill at Russian Hill Neighbors, a website for residents of the area.
Golden Gate Park: A HUGE park, over 1000 acres, or 1.6 square miles, smack in the center of San Francisco. It reminds me of Central Park, in New York City. (I've never visited either park.) You can see a 17 page, detailed history of the development of the park from its inception in 1870, till the turn of the millenium, created by the Park Service. While a bit dry, it's still interesting in that it shows maps of the park, decade by decade, as features were added and closed (or destroyed in the earthquake.) The park features gardens, lakes, an amphitheatre, bison (bison???), windmills, statues, and more. It is also a favorite haunt of the homeless, who are a perennial point of controversy for the city's citizens and visitors.
"Holy Hill" and the Graduate Theological Union at UC Berkeley: King calls UC Berkeley the "flagship of the University of California fleet". Here's how King describes the GTU in her long autobiography:
The GTU is, as the name indicates, a union of the various graduate schools —seminaries— that have taken root on “holy hill” to the north of the UC Berkeley campus. It is a tree-shaded residential area with one incursion of student life, a short block of shops, cafes, and bookstores surrounded by shingled houses and god-talk. The GTU is an independent organization that utilizes the staff and facilities of the individual church schools to put together its academic degrees. In other words, if you wish to enter the ministry, you go into a seminary; if you want an academic degree, you go into the GTU.King earned a Master of Arts degree at the GTU, so it's "home ground" for her. Religion often plays an important role in Kings' novels, but it's not much of a theme in this book, other than the "Holy Fool" theme. You'll see many Bible quotations, but little dogma.
Haight-Ashbury: Think "summer of love", think "hippies", think of a coffee shop owned by a couple named Krishna and Leila, and you're thinking of Haight-Ashbury. It's named after the intersection of Haight and Ashbury, and is notorious for its bohemian atmosphere. As the coffee shop in the book illustrates ("...the venerable Graffeo Company had deigned to suppy it with French-roast coffee...."), there's a strong trend toward the commercial mixed in with the hippie.
Fisherman's Wharf: A tourist destination. Much like Venice Beach in the LA area, it seems to exist to entertain tourists. From the street performers, to the restaurants, to the gift shops and the seals, it's a treat for a visitor. And, just as most Las Vegans avoid the strip, the San Franciscans avoid the Wharf - for the same reasons.
Santa Cruz: (The morgue where the last body was located) King lived in Santa Cruz as a young mother, and received her BA in religious studies from UC Santa Cruz.
View Santa Cruz and SF in a larger map
You can see that Santa Cruz is a fair piece from San Francisco. If Kate hadn't gone looking, they would probably never have found the last body, and solved the case.