The quality of a city's design can be judged by its population density. This is obvious when you consider that the whole reason a city exists is to take advantage of the upsides of population density. The ultimate density that a city reaches is limited by the equilibrium between the upsides and the downsides.

And when you measure population density it's best to look at the most desirable suburbs. Because the density of undesirable suburbs is primarily just a measure of the economic benefits of density, not the human happiness benefits of density. While both measures are interesting, I'm only interested in the quality of life benefits. Manila has the highest population density in the world but if you look at their most desirable suburbs it's just the same shit you will find in any nice suburb in the world. Meanwhile Singapore is nothing special when you look at average density.

My design offers density between Singapore and Manila without any dedicated high density areas to bring up the average. In fact 100% of the city surface area is walkable public space, including the buildings. It's the best of both worlds. Lots of public space and lots of private space.

Governance

It will be a hierarchical capitalist structure. The city itself will be built by a corporation upon land which they lease from a government. The districts will be leased wholesale from that corporation. The district holder will build the buildings and lease those to building operators who will build communal facilities around a speciality. For example, a woodworking building might have shared CNC carving machines and lumber milling facilities. They will then lease the remaining floor space out to individuals and small businesses who will complete a fit out of their space and operate it as they see fit. Presumably they will be taking advantage of the shared facilities within that building, but they don't have to. And finally the lowest level of the governance hierarchy is the family unit.

This hierarchical approach is important because it invites the maximum amount of competition between providers. So as a free citizen you will choose the city that suits you best. Within that you will choose the district that suits you best. Within that the building that suits you best. All organisations ossify with time because the ambitious people move on at a higher rate than the unambitious people the net effect is that all organisations become filled with less ambitious people as time goes on. By organizing cities in a capitalist hierarchy, it ensures that the most ossified components within that city lose customers as quickly as possible and therefore die and leave space to be rejuvenated as soon as possible.

Why leases? Because leases allow value to flow up. When a developer sells a building the new owner will capture the value of investments in nearby buildings made by other building owners or the infrastructure investments made by the developer. Selling of buildings or districts is like selling of shares in your company. Selling a few is okay but sell them all and you no longer have any stake in the future of your company. The ideal form of funding is loans since it doesn't reduce the incentive to improve the product. Some sale of shares is often necessary but selling all of them means selling your soul and that's what almost every city in the world has done.

Design

Of course the free market will decide what it wants. This is just my prediction for what the winning formula will be.

Each level inset from the one below

This enables dramatically more sunlight, while only giving up roughly one third of the floor space that you would get if every level had the same footprint. And the demand for floor space diminishes as you go up. Apart from the top level which receives the benefit of prestige. So this shape naturally fits demand.

All exterior space accessible

This does significantly increase the cost of construction primarily due to the increased cost of waterproofing. However, land values in dense cities are easily high enough to justify paying it. And to some extent the exterior roof space of a building is the most premium location to have a public area because it naturally acquires a degree of privacy, without closing people in.

Walk over buildings

By enabling people to walk over a building it makes the city more navigable since no matter where you are you can easily walk through a rooftop and get a perspective. Now this doesn't benefit the building owner, however this is why the district manager constructs the building because it is the district that benefits from this feature. The building owner has a secondary benefit in that when people walk over the building they become exposed to the community that occupies it and thereby might become interested in leasing a space within it themselves.

Max 5 stories

Any larger than this and a building starts to dominate its space too much. And it ends up reducing the value of the surrounding buildings. In some cases, this might be what you want if the building serves some sort of important purpose and it was going to be surrounded by parks anyway. In current cities, people build as large as they can because the negative externalities on the surrounding properties are not theirs to pay. But because the district is all developed by one person, they will seek to maximize the value of the district as a whole, not any one building in particular.

Canals between districts

Canals are the most efficient form of heavy transportation and have two additional benefits. A, they are beautiful. And B, they are quiet.

Tunnels between districts

While canals are good for heavy transport, they do not allow high speed movement. For that we have tunnels. This is the main way that humans will commute between districts. I expect commuting between districts to be relatively rare because people will work close to where they live. Also most of their hobbies will be close to where they live. I expect most people would use this transport network once a week.

Ship goods to a foyer rather than direct to house

With one foyer per building and roughly 300 people per building, it will not be overloaded. And I think lots of people will enjoy the excuse to bump into neighbors.