I've always considered it to depend mostly on whether we're talking about the current location or not. So if we're actually in San Francisco metro area and I t

I've always considered it to depend mostly on whether we're talking about the current location or not. So if we're actually in San Francisco metro area and I talk about "San Francisco", I probably mean the city proper. But if we're in DC and I talk about "San Francisco", I probably mean the metro area. Or, commonly, I actually mean somewhere specific but I don't expect my listener to know the more specific areas, so I just say "San Francisco".