Take off your blindfold. Look. This is Kowloon Walled City on the scale of New York's five boroughs.
To start with, Kowloon's Walled City would have had about 1,255,000 people if it had been a square Kilometer. New York City is about 789 square kilometers. That puts the likely population of Down New York at about 990.2 million. If you want to be able to comprehend that number of people, it's almost thrice the total population of the United States, or about a Tokyo's worth of people shy of the population of India.
And they can all fit within the land area of New York City! It just goes to show what you can do with ultra-dense urban planning. Or non-planning, as the case might be. There's no zoning commission here, no building codes, no inspectors. All the buildings were thrown together as closely as possible. They have to be; in this world everything besides this one lucky island complex is fetid swampland under high global temperatures. Until the swamps are drained and the malarial mosquitoes are banished to the outlands, the city could not expand outward. Sure, there's money to be had in building on swampland, but until the lawmen come in and impose order, there's nothing to prevent your business victims from tearing you to pieces.
But the lawmen won't come, and the Municipal Services people won't come and build anything, and the firemen won't come except by helicopter, because venturing into the vast labyrinth of Down New York is a surefire way to get lost. You want to escape your creditors? Want to run from the gang you quit yesterday? Come to Down New York and get lost. Your pursuers will never find you. Nor will anyone you know and love. You'll have to build your life from scratch here. That's the price of escape.
It's easy to build a new life here, one you get the hang of it. Just find or make something to sell and set up shop. No regulations! You can catch rats and sell them as dog meat and nobody will fine you! They'll just avoid your business. Word of advice: try cockroaches. That would be a novelty. Rat is one of the main sources of food in Down New York, along with a small trickle of wild boar form outside, and rice from the paddies of Long Island. Vegetables are grown on the rooftops and fetch lower prices than you would expect. Partly because there are so many rooftops, partly because they're grown right next to the garbage piles that adorn the roofs of a city without regular trash pickup. You can also try your luck with the feral chickens that roam the rooftops. Just watch out for the ones carrying objects in their beaks. These objects are nearly always chosen from the garbage piles to inflict maximum penetration to human skin. The chickens are mean.
Every once in a while, a Family will get enough money to purchase the aid of their neighbors, and they will bag the junk and make a great journey across the rooftops to the river, where they will fling the garbage into the water and think of it no more. They don't need to think of it anymore. The waters of the bay will dissolve the trash before it gets far. Families that live near subway stations will throw their garbage down the stairs in hopes of blocking the entrances, but the gangs try to make sure that they are kept clear.
...
In a city that is a logistical nightmare, everyone has to figure things out on their own. No help from above. The landlords cleared out a long time ago after they realized that they'd created a stinking mess. They live on an island constructed from the garbage the city throws out. They do not care to know the state of their buildings, only that the money is rolling in. Average rent per person per room is $35, and even at this low price, the landlords are immensely wealthy. A city of 990 million people is a cash cow for anyone who can get even a tenth of the people paying rent to them.
Which means that the landlords pay proxies to compete for shares of the city. This is accomplished by violence. In a city with no effective laws, the only way to control territory by force is with weapons. And so, if you choose to venture below the ladders that connect the rooftops, onto the stairs that connect one end of the city to the other, you will occasionally encounter a growling masked person with a knife in each hand. They are looking to scare away people in order to claim a spot as their own, slowly moving the border of a gang lord's territory this way or that way, or being shoved back. Remain passive. They may come over to strike, but very likely they know you. Very likely they live in your building and you have met once or twice. They, like you, are scared to move in the labyrinthine alleyways that pass for streets in this place. They, like you, have probably never ventured far beyond their own building complex. They know that they'll have to return home and face the wrath of your friends and family if they kill you. Family networks are powerful things in this city; besides the passenger pigeons, they are the best way to spread information quickly. Any masked person who stabs an unarmed, unmasked one will have their reputation sink like a stone. And don't think the alleys are anonymous either. In a city of 900 million people, there is literally always someone behind a wall or window who can see or hear your actions.
This is why gang members don't carry guns. The walls are flimsy, the alleys are narrow, and any stray bullet WILL hit someone. That ruins the reputation of the entire gang. Their members become targets of the kin networks, and vanish one by one. A rival gang moves in promising not to use firearms. This has happened enough times that there is effectively a blanket ban on guns in the city, one of the few regulations that holds true from Bronx to Brooklyn.
The gangs treat the abandoned subway tunnels as an exception. Don't go down there without a riot shield and a big dog.
...
Inside the buildings, a typical apartment complex has 35 square feet per person, with which they can do... whatever. Machine shop, brothel, restaurant, living space, library, sometimes a combination. There are plenty of restaurants where you can pay for sex, and plenty of hairdressers that let you check out books, or living spaces that people use to house their power tools. But each room is 35 feet square and tends to stay that way, because everyone is scared of removing a wall. Nobody has any idea which wall is load-bearing when the place has no blueprints. Removing a wall will get you in serious trouble with your Family, because they have to share the same building as you.
In the vast expanse of the city, your Family is how you survive. Whether you build it out of a group of friends, or you're born into it in a musty bedroom on a stained mattress, it's what keeps you alive, physically and spiritually. Your Family pools the money to pay the rent, organizes lookouts for gangs and chickens, catches rats, rotates the tasks for tending the vegetable gardens, checks the walls for structural damage, replaces broken windows with shutters, sells products, and so on. There's no help from outside, so it's up to you, as a member of your Family, to contribute to collective survival. Better hope you're on good speaking terms, if you want the work to go smoothly. A respectful Family is a happy Family, and a happy Family is a strong Family.
You will enjoy the fact that in a Family, you will never feel alone and abandoned. You will dislike the fact that, in a Family, you can never really get away from people. This is a bit of culture shock for people arriving from the Center, who are used to being alone in a city of millions. There's no space for that here. It might feel a little claustrophobic to you, but trust me, this is a GREAT place to raise children. Having adults and older kids around all the time means that no single person has to shoulder the burden of raising your child. You've got your village in a box and ready to go!
Contents may vary based on history, whim, and the capability of previous leaders to prevent bad habits from taking hold.
Members of Families distinguish between clan ties and blood ties by varying the formality of how they address each other. For example, in Ciudád Patagonia, Family members related by blood will use the formal "Usted" to address each other, and "Tu" for everyone who isn't a blood relation. Similarly, in the Franklin complex, family members not directly related will use "bro", "sis", "mom", and "pop" to address each other, while reserving the more formal versions of these words for direct blood ties. In this way, it is possible to have five moms while having only one Mother, and a hundred bros but only a few brothers. Other English-speaking families prefer to use Aunt and Uncle for unrelated adults, and words like "buddy" or "amigo" for unrelated peers. Some places split the difference and base their forms of address on how close people feel to each other. For example, the adults who do most of the work to raise a child are the moms and pops, the biological parents are Mothers and/or Fathers, and everyone else is Aunt/Uncle.
The general term "friend" applies for everyone outside the Family. This is necessary politness. Don't forget it.
...
Go up on the roof and climb the trash pile. You can see the whole of the city from there. All 990 million people. Where did they come from? Most crowded in here when the coast flooded and the food supply failed. Safety in numbers! An opportunity to re-build on the ashes of old New York! A safe hill amid the flood waters! Those banners drew them from across the world. In this world, this is most of what's left of America. There are scattered villages beyond the Appalachians, but nothing south of the Ohio River. Reports filter into the city from far across the plains that other cities and villages exist, but nothing formal has reached the mayor yet, so who can say? Trade exists almost entirely within the city. You've got almost a billion people, 1/3 of whom are from South America, and half of Brooklyn is currently called Ciudád and has its own currency, backed by rumors of hidden gold. That's enough financial surface area to maintain a monetary economy. The Mayor is content as long as the money keeps flowing.
The mayor of Down New York is not the ruler of 990 million people. He has an arrangement with the gang lords, but he directly controls the areas closest to City hall. These places have municipal services, trash pickup, police officers, and reputable food. The buildings are better-regulated and less dense. You want a spot near City Hall if you don't want to deal with the requirements of having an extended family. There are fewer taboos and traditions here. More personal freedom. More chaos, until the cops show up, and then order comes down hard. Not a good place to live long-term unless you like flush toilets. Still, the mayor is valuable, because his government guarantees the Dollar. Imagine if everyone had to barter for everything! That would make restaurants impossible.
...
Now, put your blindfold back on, and I'll lead you back home. Trust me. I don't want you coming here without me. I don't like seeing ants jump into bowls of sugar water, either. If you try to draw on the life energy of this place you'll be obliterated. You are not nearly a strong enough Shaman to handle this place. We'll come back after I show you Up New York, how about that?