The Tenderloin of San Francisco, California is an area of high density urban blight in the heart of San Francisco. Supposedly this name came from the fact that in the past police officers were paid more to patrol this seedy district and consequently were able to buy better cuts of meat. The 'loin is astonishingly close to the Union Square tourist and shopping area. This provides for lots of contrasts, such as the sight of a strung out junkie covered in urine passed out in front of a $300 a night hotel.

Vietnamese immigrants have moved to the area and have improved the neighboorhood somewhat with their shops and resturants.

http://www.sfgate.com/traveler/guide/sf/neighborhoods/tenderloin.shtml