This has been making its rounds through some of the nerdier blogs. Its a night club map of Harlem drawn by Elmer Simms Campbell, one the first African American cartoonists to be published nationally. The map was drawn in 1932 at the tail end of the Harlem Renaissance, which resulted in the first real burst of african american art and media within the U.S. The detail of the map is amazing, definitely worth a good look.
"The only omission is the location of speakeasies, but since there are about 500 you wont have much trouble."