How is a neighborhood born?

In a small pocket of the Bronx, the answer involves rising rents, a civil war and an air traffic controller at Kennedy Airport.

To see for yourself, zoom in with Google Maps near the Bronx Zoo, past Van Nest, Bronxdale and Morris Park. Get closer, and another label appears:

L I T T L E     Y E M E N

This neighborhood exists on the map partly because a Yemeni air traffic controller, Yahay Obeid, named it, by reporting that a place was “missing” from Google Maps, and submitting a suggestion for what it should be called. The name made sense, he thought, as more and more Yemenis were moving there — like those priced out of other neighborhoods or immigrants who had fled Yemen’s civil war.

After submitting the name a few times, and working with a reporter on an article about the area, Mr. Obeid checked again.

“Boom, within a couple of weeks, it was on the map,” he said.

It’s a New York pastime to gripe that neighborhoods are invented and defined by real estate brokers, developers and other city gatekeepers. But the more interesting truth may be that they are also reinvented and reinforced, refracted through race and class, by us: by the air traffic controller who lives in Little Yemen, by the Manhattan community manager who’s sure his constituents live in East Harlem — and not “Upper Carnegie Hill” — and by the Brooklyn residents who decided to name a relatively flat piece of land Boerum Hill.

A name has power. It can foreshadow who will be moving in. By itself, it can conjure so much: gentrification, displacement, inequality, status. When we argue over names, or even invent new ones, we may be trying to exert some of that power — or lamenting that others have more power than we do.

We asked New Yorkers themselves to map their neighborhoods and to tell us what they call them. The result, while imperfect, is probably the most detailed map of the city’s neighborhoods ever compiled:

As of publication, it includes more than 350 distinct neighborhoods, based on more than 37,000 responses. (The New York Times also contacted all 59 community boards and all 51 city council members to elicit responses from every corner of the city, and also incorporated some responses from a 2015 survey by DNAinfo.)

On the maps in this article, brighter solid colors signal agreement on what the area is called. Blurrier areas signal disagreement or uncertainty. Many blocks are called by three or four or even five different names. But when we stack all the drawings on top of one another, the picture that emerges is remarkably coherent.

It shows a city with a Hunts Point and a Hunters Point; with a Times Square and a Dimes Square. It has an Ocean Hill, a Sugar Hill, a Clinton Hill, a Cobble Hill, a Carnegie Hill, a Boerum Hill, a Rose Hill, a Richmond Hill, a South Richmond Hill, a Todt Hill, a Vinegar Hill, a Lenox Hill, a Forest Hills, a Cypress Hills and two Murray Hills. It has at least three Chinatowns.

Neighborhoods are not forever. Some stay, some change and some disappear. The borders you see on Google are not “official,” and neither are the ones used by real estate companies like StreetEasy. Even the city itself purposefully does not have an official city map of neighborhood borders.

“It’s not our place to define them,” said Casey Berkovitz, a spokesman for the city’s Planning Department. “We leave that up to New Yorkers themselves.”

Mr. Obeid is one of those New Yorkers who did just that.

“When you Google ‘Yemen,’ you’re going to see what goes on in Yemen, and the war — nothing really nice,” he said. “And then when ‘Little Yemen’ pops up — it’s nice.”

The Bronx Muslim Center is there. Halal meat markets, grocery stores and signs in Arabic dot the streets. Yemeni restaurants serve rashoosh, a puffy flatbread that’s bigger than their biggest plate. There are hookah shops — one is actually called Little Yemen. The local fried chicken place also serves kebab.

If you look closely, you can see a neighborhood in transition, the old and the new alongside each other: Morris Park, Van Nest, and now, Little Yemen.

“Little Yemen gives hope to big Yemen,” Mr. Obeid said.

Sharp borders or the swamp and the expressway

Our map reveals two main kinds of divisions: sharp ones and fuzzy ones.

The fuzzy ones often reflect areas in transition or dispute, where there’s no consensus or where gentrification is rewriting boundaries in real time.

The sharp ones often reflect features of the landscape itself: wide avenues, highways, remnants of canals. When you cross the street, you know you’re in another neighborhood.

Like in Brooklyn, between Bed-Stuy and Bushwick:

Or farther south, around Windsor Terrace, a neighborhood wedged between a park and a cemetery:

Or in Queens, between College Point and Flushing:

Or in Lower Manhattan, between TriBeCa and SoHo. Every sharp border has a story, and the tale behind this one involves much more than the simple fact that the neighborhoods refer to street names (“Triangle Below Canal” and “South of Houston”).

Long before there was a chic neighborhood named SoHo, and before SoHo was called Hell’s Hundred Acres or the Cast Iron District or Lispenard Meadows, much of this part of Manhattan was a swamp.

To traverse nearly 300 years in one sentence: That swamp was drained by a ditch that cut across it; the ditch became a canal; a street was built on top; they called it Canal Street; that street is now a mega-avenue, six lanes in some parts, and one of the starkest neighborhood borders anywhere in our data.

Those physical features — canals and parks and highways and the remnants of glaciers — still shape much of the city and its neighborhoods as we know them today. So too do the structures we’ve created to tame and traverse these geographies, which, in turn, birth some neighborhoods and obliterate others.

For example, when Robert Moses’ Brooklyn-Queens Expressway and its snaky offshoots were completed in the 1960s, they sheared off parts of land like the crusts off a kid’s sandwich (and displaced thousands of New Yorkers in the process).

In Queens, that highway creates border confusion in Astoria, and defines the edges of Woodside and Jackson Heights:

In Brooklyn, the leftover crusts shape Greenpoint, the Navy Yard, Vinegar Hill, Dumbo, Columbia Street Waterfront District, Red Hook and Bay Ridge:

But notice Williamsburg. The expressway slices it in two.

Other readers told us something else: They said, very forcefully, that East Williamsburg doesn’t exist. (To many New Yorkers, new neighborhoods are to be met with skepticism and, at times, contempt.)

Here’s a partial list of other neighborhoods that readers said were “made up” or “don’t exist”: NoMad, NoLIta, NoHo, BoCoCa, Hamilton Heights, Greenwood Heights, Hudson Heights, Hudson Square, Lincoln Square, Two Bridges, Carnegie Hill, Manhattan Valley, SpaHa.

In “The Colossus of New York,” Colson Whitehead wrote, “You are a New Yorker when what was there before is more real and solid than what is here now.” That is, if the new sushi restaurant in your neighborhood will forever exist in your mind as the laundromat that preceded it, you are a New Yorker.

Readers told us Alphabet City used to be part of the East Village; Bedford Park used to be part of Kingsbridge; Kingsbridge used to be part of Riverdale; Clinton Hill and Fort Greene used to be Bed-Stuy; and the “Bed” and the “Stuy” used to be separate. Bay Ridge used to be called Yellow Hook, and Inwood used to be Tubby Hook. In Brooklyn, Red Hook stayed Red Hook, and Bushwick has been Bushwick (or at least “Boswijck,” in Dutch) since 1638. Before that, it belonged to the Lenape.

If all of us live in our own version of New York, disagreement should be the rule, not the exception. “There are eight million naked cities in this naked city,” Mr. Whitehead wrote. “They dispute and disagree.”

This disagreement is perhaps best seen by looking at the map from the other perspective — the places where everyone, more or less, agrees on what to call a place. Here, we’ll slowly remove the parts of the map with the most disagreement:

Then again, just because everyone else agrees on what to call a place, that doesn’t mean you have to. Your personal borders will never be wrong. Remember: There is no official “right.”

Blurry borders or why 33rd and 5th has five names

The fuzzier places — gentle gradients where, block by block, it’s hard to say definitively what is what — are everywhere.

Like in central Manhattan:

Or in this part of Brooklyn, which people called Sheepshead Bay, Midwood or Homecrest:

Or on the North Shore of Staten Island, where one reader said, “No one knows what to call this neighborhood.”

You can see the extent of these fuzzy neighborhoods by isolating them — just search for one neighborhood on the map.

For example, here’s Flatbush, Brooklyn. See this sprawl in blue? That’s very different than how Google defines Flatbush:

Let’s look closely at Brooklyn’s Prospect Heights, which has mostly sharp edges and one very blurry one:

Seeing them together, you may notice that people who say they live in Prospect Heights increasingly draw their neighborhood’s borders eastward, beyond Washington Avenue. But people who say they live in Crown Heights almost never push west.

You can almost see the border itself moving, which is reflected in readers’ comments about Prospect Heights:

In the last 20 years, this whole area has become whiter and more affluent, with Prospect Heights being the whiter and more affluent of the two. In 2000, nearly 80 percent of the area’s population was Black. Now, just over 40 percent is.

As the border shifts, more blocks are called Prospect Heights and fewer are called Crown Heights. The area becomes more expensive. Here and elsewhere, the maps reveal gentrification in slow motion, block by block.

Consider a three-bedroom, nearly $1.8 million condo for sale on Sterling Street, in the middle of our border area between Washington and Classon Avenues.

StreetEasy lists the unit as being in Crown Heights. Another company, Douglas Elliman, lists it in Prospect Heights. If the apartment is in Crown Heights, it becomes one of the most expensive three-bedroom units in the neighborhood. If the apartment is in Prospect Heights, it becomes a relative bargain for the area.

The moving borders trickle down to street level, too. A local grocery store on Classon Avenue — two blocks east of Washington,

used to be called Gala Fresh Farms.

Now it’s called Key Food: Prospect Heights.

One neighborhood grows while another shrinks.

Carving out or how high does the Upper East Side extend?

City blocks can be pawns in a kind of geographical warfare, unwittingly on offense or defense amid the churn of migration, demographic change and real estate salesmanship.

Readers told us their neighborhood boundaries were “blurred,” “rebranded,” “encroached upon,” “stretched,” “chipped away at,” “muddled,” both “semi-amorphous” and “amorphous”; that they were “mushy,” “fuzzy” and “lumped in with” bigger neighborhoods; or that their neighborhoods’ names were merely a “real estate moniker,” “invented by” agents, a “scam” or a “ploy.” Some said their neighborhoods had been “renamed,” “erased,” others “carved up.”

What does that carving look like? Consider a pair of large and established adjoining neighborhoods in Manhattan: the Upper East Side and East Harlem:

In this view, what’s happening looks very similar to what we saw in Prospect Heights and Crown Heights in Brooklyn, with one neighborhood on offense (the Upper East Side) and another on defense (East Harlem).

But there’s something else going on, barely noticeable in our map but much realer to real estate companies. To StreetEasy, the Upper East Side includes a narrow section of Fifth Avenue along Central Park’s East Side, like a gerrymandered congressional district, stretching up, up, up to 110th Street.

StreetEasy calls this area “Upper Carnegie Hill.”

Few readers identified it as a neighborhood. Those who did could not decide where it was, what to call it or how seriously one should take people who say they live there.

Xavier Santiago, the chair of Manhattan’s Community Board 11, which includes the East Side of Manhattan north of East 96th Street, was quite sure what to call it.

“That is East Harlem,” he said.

Upper Carnegie Hill exists on StreetEasy and in real estate-speak, but it doesn’t appear to have caught on with residents.

Yet sometimes the new names do take, and it’s not always real estate agents who are trying to define them.

This map of Brooklyn from 1919 is not comprehensive, but it does show some neighborhood names from that time:

That large mass of South Brooklyn is now a handful of discrete, well-established neighborhoods — Cobble Hill, Carroll Gardens, Boerum Hill — that were born, one by one, starting in the late 1950s.

A very short version of what happened here, culled from “The Invention of Brownstone Brooklyn” by the author and professor Suleiman Osman, is that residents and newcomers formed neighborhood associations, picked historical-sounding names plucked from old maps (Cobble Hill was named after a fort from Revolutionary times, for example), claimed blocks south of Atlantic Avenue that had brownstones, and rehabbed those brownstones. And the names, as they say, stuck.

These and other parts of Brooklyn went from being a place immigrant and minority families started from, to a place where white-collar professionals went to as they felt they were priced out of parts of Manhattan. And as the area got richer, these smaller, more exclusive-sounding neighborhoods replaced the once less-defined mass.

Ironically, decades later, real estate agents tried to mush them all back together into BoCoCa (Boerum Hill-Cobble Hill-Carroll Gardens), but it didn’t really take, adding it to a list of failed smushed names that includes SoBro (South Bronx), SpaHa (Spanish Harlem), SoHa (South Harlem) and Rambo (Right Around the Manhattan Bridge Overpass).

Taking this lesson, think about New Yorkers in the year 2080 looking at our map. What might they notice? What history has told us so far is that in the long run richer neighborhoods get bigger, and bigger and relatively poorer neighborhoods tend to get carved into smaller ones. Some of those then get richer, and then get bigger.

And some just disappear.

The end or accepting impermanence

When Boerum Hill was known as “North Gowanus,” a community of several hundred Mohawks found jobs building skyscrapers and bridges. Starting in the late 1920s, they settled on either side of Atlantic Avenue. Some of them called it “Downtown Caughnawaga,” an English spelling of their reservation’s name.

This tradition continues today — though little of it is visible on our map — through the millions of New Yorkers who speak one of the city’s other languages and dialects (over 700 at last count, according to Ross Perlin, co-director of the Endangered Language Alliance).

“Loisaida, an ingenious Nuyorican play on both the Lower East Side and the city of Loíza Aldea in Puerto Rico, is the rare non-English name that is breaking through,” Mr. Perlin writes in “Language City,” a forthcoming book.

There are many more secondary names, of course. El Barrio for East Harlem. Los Sures for the once-predominantly Puerto Rican south side of Williamsburg. And Quisqueya (an Indigenous Taíno name for the whole island of Hispaniola) is a Dominican nickname for Washington Heights.

These names help communities try to preserve space in a city where space is at a premium. Some names will stick — and some won’t. Mr. Obeid, the air traffic controller, knows this too.

“Another generation is going to come through,” he said. “It’s a different, diverse community.”

Little Yemen hasn’t made it onto our map yet, but it does seem to be coming into focus for those who live there.

“With the growth of the Yemeni population, I’d consider Little Yemen to be its own neighborhood at this point,” one reader wrote.

Toward the end of a discussion about Little Yemen, Mr. Obeid told a story about its reach. Two pilots were on a layover in New York, and they asked him about his neighborhood by name.

“I thought, Little Yemen has really become international,” he said. “This is amazing.”

They were curious, and wanted to visit.

So he took them to lunch in his neighborhood.

To add your neighborhood and tell us more about where you live, go here. We’ll incorporate additional responses in our map as they come in.