There isn't much to say about zones except that they determine where in your city your citizens are going to live. If you've never played the game before, the game has three different types of zoning:
An delicate balance of all three types of zones are required to maximize profits.
Residential
This is where people live.
Light residential is single-family homes; medium-density residential zones are multi-story row homes and small apartment complexes; high-density residential consists of high-rise apartment buildings.
In the image above, you can see medium-density apartments on the right and low-density family homes on the left.
Commercial
This is where people shop.
Light commercial is like gas stations and corner stores. Medium-denisty commercial will produce strip malls and superstores. High-denisty commercial zones produce high-rise towers and corporate headquarter locations.
In the image above, you can see medium-density shopping centers in the background and some low-density gas stations and such up front.
Industrial
This is where people work.
All three industrial zones produce two things: goods and pollution. Low density produces less of both; high-denisty produces lots of both; medium (as you can imagine) is in the middle. All three produce factories and warehouses of varying sizes.
In the image above, you can see two beautiful factories that would warm the heart of even the most extreme steampunk honey.
HUD: Zoning
The zoning HUD is visible when you click the little diamond-shaped icon on the main HUD bar at the bottom of the screen. There are four buttons: residential, commercial, industrial, and de-zoning (from left to right).
De-zoning
If you see a residential building in your city in a spot that you would prefer to see a gas station, you must do two things to remove the offending building from that location. Firstly, you must de-zone the area -- removing the residential zoning you laid down earlier. Secondly, you demolish the building you don't want. If you don't do these two steps in that order, when you demolish the building and go to re-zone it, it's distinctly possible that a moving crew will move in and begin building a new residential building while you're fiddling with the HUD.
Moving In
When you zone a location, massive unseen calculations take place behind the scenes. Among these calculations are three important ones to consider when first starting out: access to water, power, and proximity to other zones. If a residential zone is placed well away from the starting point of your city, it might not grow because it's too far away from commercial or industrial zones. Anything un-powered or un-watered will grow slowly -- if at all.
On the street level, you can actually watch zoned land develop. Little citizens will arrive in moving vans after the construction workers leave and you can learn all about them and their lives. They'll even talk to you if you screw up or somehow make their lives better.
Limits
Technically, you can draw a square road around the entire board and zone it all residential. That will get you practically nowhere unless you're playing multi-players with some crazy friends. Obviously, no matter how big you make a zone, there is a limit to how big the buildings within it will grow.
The reverse is also true. If you squeeze the roads together too close, they'll almost always develop, but the tiny houses they squeeze in there will be murder houses where psychopaths take their victims. So it may take a few tries, but you want to get a feel for the dimensions of factories and high-density apartments and then build your street grids accordingly.
Roads and Zones
A road that splits a zone will de-zone whatever it touches. Equally, a road that is demolished will de-zone any buildings that abut it. So any time you demolish a road, be prepared to re-zone the immediate areas on either side of where the road was.
The density of the buildings on a zone are based on several factors, but chief among them is the volume of the roadway that abuts the zone. If a zone lies next to a low-density dirt road, there is a limit to what can develop there. On the flip side of that coin, a high-density boulevard will accommodate high-rises and other superstructures.
