SAN FRANCISCO — For decades, the district south of downtown and alongside San Francisco Bay here was known as either Rincon Hill, South Beach or South of Market. This spring, it was suddenly rebranded on Google Maps to a name few had heard: the East Cut.

The peculiar moniker immediately spread digitally, from hotel sites to dating apps to Uber, which all use Google's map data. The name soon spilled over into the physical world, too. Real-estate listings beckoned prospective tenants to the East Cut. And news organizations referred to the vicinity by that term.

''It's degrading to the reputation of our area,'' said Tad Bogdan, who has lived in the neighborhood for 14 years. In a survey of 271 neighbors that he organized recently, he said, 90 percent disliked the name.

The swift rebranding of the roughly 170-year-old district is just one example of how Google Maps has now become the primary arbiter of place names. With decisions made by a few Google cartographers, the identity of a city, town or neighborhood can be reshaped, illustrating the outsize influence that Silicon Valley increasingly has in the real world.

The Detroit neighborhood now regularly called Fishkorn (pronounced FISH-korn), but previously known as Fiskhorn (pronounced FISK-horn)? That was because of Google Maps. Midtown South Central in Manhattan? That was also given life by Google Maps.

Yet how Google arrives at its names in maps is often mysterious. The company declined to detail how some place names came about, though some appear to have resulted from mistakes by researchers, rebrandings by real estate agents -- or just outright fiction.

In Los Angeles, Jeffrey Schneider, a longtime architect in the Silver Lake area, said he recently began calling the hill he lived on Silver Lake Heights in ads for his rental apartment downstairs, partly as a joke. Last year, Silver Lake Heights also appeared on Google Maps.

''Now for every real-estate listing in this neighborhood, they refer to it,'' he said. ''You see a name like that on a map and you believe it.''

Before the internet era, neighborhood names developed via word of mouth, newspaper articles and physical maps that were released periodically. But Google Maps, which debuted in 2005, is updated continuously and delivered to more than one billion people on their devices. Google also feeds map data to thousands of websites and apps, magnifying its influence.

In May, more than 63 percent of people who accessed a map on a smartphone or tablet used Google Maps, versus 19.4 percent for the Chinese internet giant Alibaba's maps and 5.5 percent for Apple Maps, according to comScore, which tracks web traffic.

Google said it created its maps from third-party data, public sources, satellites and, often most important, users. People can submit changes, which are reviewed by Google employees. A Google spokeswoman declined further comment.

Yet some submissions are ruled upon by people with little local knowledge of a place, such as contractors in India, said one former Google Maps employee, who declined to be named because he was not authorized to speak publicly. Other users with a history of accurate changes said their updates to maps take effect instantly.

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Many of Google's decisions have far-reaching consequences, with the maps driving increased traffic to quiet neighborhoods and once almost provoking an international incident in 2010 after it misrepresented the boundary between Costa Rica and Nicaragua.

The service has also disseminated place names that are just plain puzzling. In New York, Vinegar Hill Heights, Midtown South Central (now NoMad), BoCoCa (for the area between Boerum Hill, Cobble Hill and Carroll Gardens), and Rambo (Right Around the Manhattan Bridge Overpass) have appeared on and off in Google Maps.

Matthew Hyland, co-owner of New York's Emily and Emmy Squared pizzerias, who polices Google Maps in his spare time, said he considered those all made-up names, some of which he deleted from the map. Other obscure neighborhood names gain traction because of Google's endorsement, he said. Someone once told him they lived in Stuyvesant Heights, ''and then I looked at Google Maps and it was there. And I was like, 'What? No. Come on,''' he said.

In Detroit, some residents have been baffled by Google's map of their city, which is blanketed with neighborhood monikers like NW Goldberg, Fishkorn and the Eye. Those names have been on Google Maps since at least 2012.

Timothy Boscarino, a Detroit city planner, traced Google's use of those names to a map posted online around 2002 by a few locals. Google almost identically copied that map's neighborhoods and boundaries, he said -- down to its typos. One result was that Google transposed the k and h for the district known as Fiskhorn, making it Fishkorn.

A former Detroit city planner, Arthur Mullen, said he created the 2002 map as a side project and was surprised his typos were now distributed widely. He said he used old books and his local knowledge to make the map, approximating boundaries at times and inserting names with tenuous connections to neighborhoods, hoping to draw feedback.

''I shouldn't be making a mistake and 20 years later people are having to live with it,'' Mr. Mullen said.

He admitted some of his names were questionable, such as the Eye, a 60-block patch next to a cemetery on Detroit's outskirts. He said he thought he spotted the name in a document, but was unsure which one. ''Do I have my research materials from doing this 18 years ago? No,'' he said.

Now, local real-estate listings, food-delivery sites and locksmith ads use Fishkorn and the Eye. Erik Belcarz, an optometrist from nearby Novi, Mich., named his new publishing start-up Fishkorn this year after seeing the name on Google Maps.

''It rolls off the tongue,'' he said.

Detroit officials recently canvassed the community to make an official map of neighborhoods. That exercise fixed some errors, like Fiskhorn (though Fishkorn remains on Google Maps). But for many districts where residents were unsure of the history, authorities relied largely on Google. The Eye and others are now part of that official map.

In San Francisco, the East Cut name originated from a neighborhood nonprofit group that residents voted to create in 2015 to clean and secure the area. The nonprofit paid $68,000 to a ''brand experience design company'' to rebrand the district.

Andrew Robinson, executive director of the nonprofit, now called the East Cut Community Benefit District (and previously the Greater Rincon Hill Community Benefit District), said the group's board rejected names like Grand Narrows and Central Hub. Instead they chose the East Cut, partly because it referenced an 1869 construction project to cut through nearby Rincon Hill. The nonprofit then paid for streetlight banners and outfitted street cleaners with East Cut apparel.

But it wasn't until Google Maps adopted the name this spring that it got attention — and mockery.

''The East Cut sounds like a 17 dollar sandwich,'' Menotti Minutillo, an Uber engineer who works on the neighborhood's border, said on Twitter in May.

Mr. Robinson said his team asked Google to add the East Cut to its maps. A Google spokeswoman said employees manually inserted the name after verifying it through public sources. The company's San Francisco offices are in the neighborhood (as is The New York Times bureau), and one of the East Cut nonprofit's board members is a Google employee.

Google Maps has also validated other little-known San Francisco neighborhoods. Balboa Hollow, a roughly 50-block district north of Golden Gate Park, trumpets on its website that it is a distinct neighborhood. Its proof? Google Maps.

''Don't believe us?'' its website asks. ''Well, we're on the internet; so we must be real.''