Zones are sections that are designed to reserve land for a specific kind of building.
Why are they there?
Basically, they exist in order to beautify the town and ensure things don't get all muddled up and ugly.
Who makes the zones?
The city's mayor.
What is a green zone?
A green zone comes in three different shades. They are reserved for residential buildings only. The lightest shade is for the high class residences and the darkest for the low class, with the middle class residences reserved for the medium colored shade.
Why can't I just build any residential building on any green shade?
If you were living in a high class residential building, would you like to have low class right beside you? When you mix all the classes together, it brings property values down and people will just move out or never even move in. You have to keep each class separate to keep them happy (particularly the high class).
What is a light-blue zone?
A light-blue zone is a zone strictly reserved for big commercial buildings like company headquarters, TV stations and commerce in general, like stores or movie theaters.
What is a dark-blue zone?
A dark-blue zone is a zone strictly reserved for office buildings.
What is a yellow zone?
A yellow zone is made for industrial buildings. In normal circumstances, the mayor puts it far away from everything because of the polution which would cause the people to move out of town.
What is a white zone?
A white zone is a zone strictly reserved for civic buildings and monuments.