The always useful David Rumsey Map Collection has a neat map of San Francisco's Chinatown from 1885 available as an ultra-high resolution download. It includes helpful notations from the town fathers on locations where opium, gambling, and prostitution were known to be active. There's more than a whiff of casual racism about it, but it's an awesome resource for a pulp game.
As an aside, I've been doing quite a bit of reading about the history of sideshow gaffs. Most of that material is contained in books about traveling shows and the circus, and it's amazing how pervasive racism was in that environment. At the same time, it's a very strange, uniquely American brand of racism that schizophrenically alternates between xenophobia and xenophilia for various groups.