Cities: Skylines 2

While players don't construct zone buildings in Cities: Skylines 2, their actions have a direct impact on when those buildings go up, what kinds of buildings appear, and how quickly they upgrade.

Upgraded buildings are a universally good thing in Cities: Skylines 2. While they use a little more water and power, upgraded residences can fit more families while upgraded businesses have more high-paying jobs available. In both cases, property values go up, and thus so do taxes paid to the player. The only real trouble is convincing citizens to make these upgrades.

Upgrades and Disposable Income

Cities Skylines 2 Upgrade Building — A level 5 commercial business in Cities: Skylines 2.

In the first game, the requirement for an upgrade was directly based on education. In the sequel, education still plays a major role, but it's more indirect now. The requirement for upgrading a building in Cities: Skylines 2 is disposable income. The more money a resident or a business has to spare, the more they can spend on upgrading their building.

The way to get this disposable income (or profit) depends on the zone type.

Residential

Jobs that require better education levels provide more money.
Money paid to the city is money not spent on upgrades. This includes service fees and property taxes.
Instead of demanding taxes, players can offer subsidies to residents. Residents are perfectly happy to spend this money on building upgrades.

Commercial

Commercial businesses need access to a large customer base to make a profit, and they can spend this profit on building upgrades.
Profit margins also increase with worker efficiency, and efficiency goes up when workers are happy.
Like with residential buildings, players can use taxes, fees, and subsidies to encourage or discourage commercial growth. Players can do so for commercial buildings in general or each commercial industry specifically.
Commercial businesses must pay more for goods produced off-map, so a strong industrial sector will boost commercial business profits.

Industrial/Office

Taxes, fees, and subsidies also play a role in industrial business profits.
Industrial zones need access to raw materials, materials they pay for much like commercial businesses. Raw materials come from specialized industrial zones, so try to build at least one of each to bring industrial costs down.
A nearby cargo terminal for ships, trains, or planes can also keep costs low.
Worker happiness is just as important for industrial efficiency as commercial efficiency.
Office businesses require "immaterial" goods instead of material goods. This means they need a strong internet connection instead of a good road network.
The amount of local demand for industrial products has no real impact on industrial business profits.

One last requirement all zone types need is time. Residents and businesses need time to save up enough money to buy an upgrade, especially if the building they occupy is in a high-density zone. If players have done everything they can to improve an area, a little patience may be the only thing they still need.

How to Boost Happiness

Cities Skylines 2 Happiness — Sources of happiness revealed in Cities: Skylines 2.

Happiness (closely related to another stat, Well-Being) is among the most important numbers in the game. A happy population works harder, complains less, and is less inclined to move out of the city. Players must provide their citizens with every service and protection they can to keep this number up. Impacts on happiness include:

Average wealth
Reliable mail
Reliable internet
Reliable healthcare
Plenty of entertainment
Plenty of education opportunities
Plenty of free time
Low taxes
Large homes
Protection from fire
Protection from crime
Protection from pollution
Protection from disasters
No electricity failures
No water failures
No sewage backups
Timely body disposal

In short, every service players can provide has an impact on citizen happiness. If players can keep on top of every demand Cities: Skylines 2 throws at them, both happiness and building upgrades will follow.