The residential zone is the name given to zones that allow for residential development to occur. The zones' color is green but in older SimCity titles it was red. Houses, apartments, tenements, and other structures that provide housing for the Sims will grow on these lots if the conditions are right; such as having water and a good environment. Without these zones, a city will not be able to sustain a population.
There are 3 types of residential zones: low density,medium density and high density. The density describes how many Sims can live on a given lot. For example, low density allows for development of houses and mansions, whereas high density will allow for the development of tenements and large apartments.
The density of the lots will not affect the wealth level of the Sim that lives on it (all 3 wealth levels are able to develop in all 3 different densities). When a building is completed, moving trucks will spawn near the site, and the new inhabitants will move in.
Power is the basic need for residential zones, but with more services provided, richer Sims will move in. There are three kinds of people who can live in residential zones: low, medium, and high wealth. Low wealth residents tend to move in anywhere as long as there is available power (as well as water in SimCity (2013)) and space, but middle and high wealth residents require more services, such as sufficient water, education, healthcare, amongst others in order to meet their demands.
In SimCity 4, the player can now adjust their tax rates individually, without affecting the others. The default tax rate is 9.0% for all three wealth levels, but the levels can be adjusted accordingly, to a maximum of 20.0% and a minimum of 0.0%. Of course, taxation rates will also affect demand, depending on how high or low the rates are set. Generally, higher rates reduce demand, whereas lower rates increase demand.