In a dense city, we're talking thousands of simulation units (factories, businesses, etc.) each with their own resources and rules, tens of thousands of agents (cars, pedestrians, sewage, etc.), dozens of maps (air pollution, water table, etc.), and other simulation components all interacting in real-time on a mid-range home computer.
 
It's a client performance issue. The memory required to store information of more cities and the performance required to show even bigger regions and additional cities is too much. 16 was just the number that met the budget. Sorry for jumping the gun!

We're still working on infilling between buildings with appropriate stuff. Asphalt, concrete, storage yards, etc, depending on what sort of buildings are nearby.
 
Buildings come in at different densities - low density buildings (like standalone houses) have space between them. By the time you get to middle density, buildings are packed much more tightly. High density buildings are mixed. Some have plazas or other spaces around them, some are tightly packed.

Universities don't contribute money directly to your bank account as a Mayor, the way that taxes and selling resources does. However, educating your Sims has a lot of benefits that go well beyond making income.
 
Educated Sims are less prone to lighting their houses on fire. They install solar panels on their houses to reduce the amount of electricity that they require. They also use less water as well. They are healthier (less likely to get sick), they are less likely to resort to crime (prevent crime, don't treat the problem with police!).
 
But that's just how education affects your residential areas. Education also affects your industry, and this is the part that really gets me excited. If you want High Tech industry you're going to need education. The influence from education buildings (particularly the Community College and the University) will cause industrial buildings to go from dirty, polluting brick buildings to flashy, gleaming metal and neon high tech buildings that pollutes less. I love the look of a high-tech city - it competes with the Gambling town for my favorite city type in the game.
 
Another cool thing about education is that it can be shared. Students from one city can visit a University in another city to be educated there. The benefits that a University provides are shared with the entire region, so the guy with the University town is going to be very popular indeed!

As your city grows you'll be introduced to finer tax controls. Before your city is formally incorporated, by placing a Town Hall, there's no tax controls (because, technically, there's no city government!). Town Hall gives you the option to adjust taxes, but only universally (for RCI and all wealth classes). Once your city grows a little and your Town Hall blossoms into a City Hall you'll be able to control R, C, and I taxes separately. Then, when you add a Dept. of Finance to the City Hall you'll get the ability to tax each zone type and wealth class individually. Sims respond to taxation differently, so it's possible to find a sweet spot where they're grumbling about high taxes but they're not being run out of town yet.

Will there be arcologies?
 
[–]MaxisGuillaume 2 points 2 jours de ça
Yes!

Bridges get created automatically with the right height when you drag a road or an avenue over water (with enough space for boats to go under them) while cruise ships come to your cruise ship terminal (which is really a module off the ferry terminal.)
 
The cruise ships bring in medium and high wealth tourists to the attractions in your city, things like landmarks, casinos, stadiums, etc...
 
You can make a curvy bridge if you want, we won't stop you! If the bridge goes over a valley, you can definitely build a road underneath, as long as there is enough space.

When 301 of the most advanced model, the "Launch Arco," are built, an "exodus sequence" starts in which all Launch Arcos blast into space.