Whenever noir (the darker, seedier and urban side of the mystery genre) is mentioned, as specifically when film noir is mentioned, the city that comes to mind first is Los Angeles. At the time when the genre was in its infancy and was lumped together with all detective mysteries as "detective fiction" San Francisco was the setting for quite a few mysteries. The best known of them is probably The Maltese Falcon by Dashiell Hammett and later immortalized by the Warner Bros.'s 1941 film starring Humphry Bogart.
I've seen the 1941 film starring Humphry Bogart more times than I can count, though it has been a number of years since my last viewing. Somehow in all those times watching I never picked up (or at least, failed to remember) that the story takes place in San Francisco! Dashiell Hammett's descriptions, though, of the city and its neighborhoods made the city come alive more than it did for me in the film. It was also interesting to me that the story was published in 1929 which gives an insightful view of a city right on the edge of economic hardship at the dawn of the Great Depression.
Sam Spade did not remind me at all of Bogart in his depiction and his dialogue. He's actually far more elegant a speaker in the book than he is in the film (or at least than I remember him being in the film). In fact the dialogue throughout the book contains phrases that have fallen out of use in States but are still in use in Britain and a few times I even double checked the book's publication location to see if it were an import; it isn't. With his careful way of speaking and his desire to avoid trouble whenever possible, Spade ended up reminding me a great deal of a 1920s Dirk Pitt!
The one main flaw with both the book and the film is Brigid. She is portrayed as such a poor actress than I'm always amazed that Spade falls for her tricks for so long. All the way through the book I wanted to slap him on the back of the head and scream "pay attention!" because her ploys are so obvious. Oh well, what can one expect from a proto-femme-fatale?