Taking a walk through Chinatown is to walk through space and time. Now, I know that concept sounds like something out of the Twilight Zone, but let me explain. Walking down Chinatown feels like walking through a timeline of the "Chinese-in-America Experience." Chinatown's urban fabric covers the full spectrum of this experience - from the things that are so obviously Chinese (family associations) to the things that are almost fully Western yet are still somehow inevitably ethnically distinct (Ten Ren). The former is often, though not always, older, and the latter is often, though also not always, more recent.
But as time passes by relentlessly, Chinatown somehow manages to capture every single frame of its history so that very little is lost. You can see it not only in old and new buildings, but in the preservation of alleyways, the oral transfer of history from Chinese elders to their children and grandchildren, the work of countless community organizations, etc. Look for these signals, and as you move through the space of Chinatown, so will you also move through its time, or, its past, present, and its future.
That's why I chose this picture to exemplify what, to me, makes SF's Chinatown unique. It's a mural depicting Chinese history in America on a building which will serve as the future site of the Central T Subway. Even as Chinatown moves forward, it refuses to let go of its past.
Unfortunately, if I didn't tell you this, or if you didn't go on a tour with one of the locals as your guide, you might've missed all the clues that point to this unique quality of SF's Chinatown. Instead, you might just think, "Oh, this is Chinatown. It's very...Chinese." And tragically, all those details of history would be lost to the shallow understanding that Chinatown is simply an ordinary, generic expression of ethnicity. But it's not.
It's a living, breathing history not recorded in books (though I'm sure there are many you can read) but embodied in space. You just have to learn how to read it. So talk to somebody about it. Ask somebody about it. I'm sure you'll find plenty of people who'd love to tell you about it.