Many San Franciscans act as if they don’t really live in a big city. We’re told it’s a collage of neighborhoods and diversity. Affinity groups and shared cultures. Small villages within a single boundary.

In fact, this wasn’t always the case.

The proof is in “Boomtowns: How Photography Shaped Los Angeles and San Francisco,” a thought-provoking exhibition open now at the California Historical Society on Mission Street. It shows how these two cities came to be, and how they presented themselves to the world.

The photos selected from the society’s archives by curator Erin Garcia are engaging, to be sure — you can’t not be pulled into the aerial view of San Francisco after the 1906 earthquake, shot from a camera hanging from kites 2,000 feet in the air. An 1880 postcard with its Edenic depiction of a a vine-shrouded home and the caption “Los Angeles in January” shows why generations of families from the East and Midwest remade themselves as Angelenos.

Yet what strikes me about the San Francisco depicted here is that from the start, it’s portrayed as an urban landscape. Los Angeles in many ways was conjured up by business interests, railroads with seats to fill and developers with land to sell. San Francisco was a fluke of the 1849 Gold Rush, born of necessity and then eager to be the economic centerpiece of the territories beyond.

That’s the impression in one of the oldest, eye-popping highlights of “Boomtowns,” an 1864 panorama by Carleton Watkins. It’s a view from the peak of Nob Hill presented in five “mammoths,” at 18 inches by 22 inches the largest photographs that then could be made, with Mission Bay on the right and Alcatraz on the left.

This isn’t some quaint hamlet; it’s a metropolis on the make. We see sidewalks and streetlamps, and imposing brick churches amid the grid of wooden structures. The waterfront is a place to do business; the sandy slope in the foreground on the left isn’t nature being preserved, it’s a building lot that no doubt was soon filled in.

On a much smaller scale, consider two 1870 photographs of Montgomery Street.

Nothing is taller than three stories — a far cry from the towers we see today, or the “narrow canyon between skyscrapers” referred to in the 1939 guide to San Francisco published by the Federal Writers’ Project. But the photography firm Lawrence & Houseworth crop the three-story blocks so that they fill the image. We’re looking at robust prosperity. A place to do business, even then.

Such shots can be dismissed as commercial boosterism, yet the matter-of-fact mentality continues in the 20th century imagery. There’s a wonderful Rovere Scott photo of the Financial District skyline as seen from the bay in 1936. What’s shown seems romantic in hindsight, a masonry cluster of such now-revered architectural peaks as the Shell Building. At the time, I suspect, the intent was to show concentrated sophistication — a city on par with anything back east.

More Information “Boomtowns: How Photography Shaped Los Angeles and San Francisco, Selections From the California Historical Society Collection”: 11 a.m.-5 p.m. Tuesdays-Sundays. Through March 12, 2019. California Historical Society, 678 Mission St., San Francisco. 415-357-1848. www.californiahistoricalsociety.org

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Or take in a 1925 photograph of Nob Hill’s summit by Ansel Adams. He’s legendary now for photographs of Yosemite and the wonders in other national parks. But this is a compacted urban scene, a meticulous stack of rectangles that conclude in the Mark Hopkins’ tall crown.

Even photographs that emphasize incongruities suggest a city at ease with itself.

Two of my favorite shots capture the tight collision of scales, of worlds. One is of Telegraph Hill, taken by Laura Adams Armer around 1910. The foreground shows shadowed, residential cottages nestled against a curved street. Below and behind it, in clear light, is the working waterfront capped by the Ferry Building. Mountain hamlet and industrial port, each confident in its realm.

Another, “Haas Wood and Ivory Turning Works, 64 Clementina St.,” is one of the 10 Minor White photographs in the show. They’re all good, but this one’s startling — a two-story blue-collar enclave smack against the thick concrete ramps leading to the old Transbay Terminal. Old and new couldn’t be more jarring. White presents it as a cool-eyed curiosity, not an indictment.

That’s how big cities are, right?

This shrugged perspective would be challenged today. Planners emphasize the need to respect context, so that fresh waves of development don’t overwhelm what already exists. In many of San Francisco’s more settled neighborhoods, the smallest addition to a house can trigger hearings and lawsuits.

I understand the resistance to change. After all, “Boomtowns” ends before the urban renewal efforts that showed how destructive “renewal” can be. An exhibition moving forward from the 1960s would show such work as Ira Nowinski’s photos of the razing of blocks south of Market Street for what now is the area around the Moscone Convention Center.

But if we cling too much to the past, or insist that an altered skyline must inevitably be a blight, we deny the nature of how cities evolve. The challenge today isn’t to lock San Francisco in place, but to find ways to make the ongoing boom beneficial to all.

Never an easy task.

There’s more here than a cool bunch of old photographs. As “Boomtowns” shows, San Francisco is a city of complicated revelations. That’s what makes this metropolis so fascinating, no matter the frustrations of the moment.

John King is The San Francisco Chronicle’s urban design critic. Email: jking@sfchronicle.com Twitter: @johnkingsfchron