Pedestrians walk past the Amazon Spheres in downtown Seattle on a rainy day. (Ted S. Warren/AP)

Thomas Kohnstamm is the author of “Do Travel Writers Go to Hell?” and the forthcoming novel “Lake City.”

As New York City and Crystal City in Virginia prepare for Amazon to plant its new headquarters and thousands of employees in their areas, take it from a rare Seattle townie who’s lived in the same house he grew up in since the 1970s: Get ready for a lot of change — some for the better, but certainly not all of it positive. I have never found Seattle at once so cosmopolitan and so painfully one-dimensional.

Many Seattle old-timers lament a bygone era, before Amazon took over, when Seattle was cooler, chiller, more affordable, more creative, friendlier to artists, less corporate, what have you. Our city’s history is short. Our culture is insecure, ever-shifting and always susceptible to being overrun by an influx of arrivals. The old-timers are correct: We have lost many things.

This hasn’t been all bad: Before the Amazon explosion, much of Seattle was vanilla. Everything shut down early. There was nothing for teenagers to do. In a city that has rain for nine months out of the year, no one thought to have indoor family recreation that was also enjoyable for the adults. Iceberg lettuce was the main vegetable. People bought all their clothes at REI. Red Vines and boiled hot dogs were the height of concessions in the city’s public spaces. Uptight old hippie neighbors screamed at you for letting your intoxicated father-in-law play an acoustic cover of “Blackbird” in your backyard at 10:02 p.m. (Okay, that was last August.)

But you could also afford to live in many parts of town, even with intermittent employment. And you were left alone to do what you wanted, so long as you followed the unofficial Seattle rules of humility and outward restraint. You had freedoms behind closed doors or somewhere out in the great outdoors that surround Seattle.

It’s unfair to attribute all the seismic change since then to Amazon alone. (Amazon’s founder and chief executive, Jeffrey P. Bezos, owns The Post.) When Microsoft went public in 1986, it created the equivalent of a millionaire per block. Public offerings for Starbucks, Amazon and tech companies followed. In the ’90s, the popularity of our local music scene and changes in communications, media and transportation further connected Seattle with the rest of mainstream American culture. When I was away at college in the mid-’90s, it seemed like I returned to a different city each winter and summer vacation.

I moved back to Seattle for good in 2006, and, even at that point, everyone was still wondering when Amazon would turn a real profit. As we started to recover from the 2008 economic crisis, however, Amazon took off. It expanded into the South Lake Union neighborhood in the city center and ramped up its workforce. Its share price, the local economy and real estate market went into overdrive.

Seattle is now the biggest company town in America, and Amazon holds about a fifth of the prime office space in the city. The company’s global employment numbers are catching up with Seattle’s population, and the company has recently proved its ability to overpower the city council and mayor on matters big and small. If you go to South Lake Union at lunchtime, you’re hard-pressed to find a person on the street not wearing an Amazon badge as they dart between the Berlin-style kebab spot and the quinoa bowl food trucks.

Restraint, humility and their cousin, drabness, are a thing of the past. New Seattleites do un-Seattle things, such as jaywalk or get bottle service at rooftop bars (which would have seemed like an awkward L.A. imitation just a few years back). The local car of choice has morphed from an old white Subaru with a roof rack and a dented door to freshly leased BMW SUVs. Maseratis are the new Corolla.

My once-residential neighborhood in North Seattle is home to JuneBaby, the country’s best new restaurant last year, according to people and publications that claim to determine those things. Down the street, there’s a soon-to-open subway station that will whisk you downtown or to the airport. Even the used-car and vice corridor of Lake City Way is transforming its seas of cracked parking lots into six-story condo blocks with poke and bubble-tea spots on the ground floors. A house on my block went from a junkie flophouse to an uninhabited arson job to a million-dollar starter home in just three years.

But as any old Seattleite who lived through the Boeing Bust in the 1970s can tell you: beware of monoculture. What Seattle has gained in cultural diversity, it has lost in class diversity. My block itself has gained white-collar professionals from across the United States, the Philippines, India, Brazil, Britain and more. But almost every single one of these breadwinners work in technology — most for Amazon.

Still, I wonder: If the company were to stumble, how many of these newcomers would have any compunction about catching the next flight to the Bay Area, Austin or Boston?