The Underlying Mechanics

We performed several experiments on Theotown, and found some stuff. But first you need to know:

Prerequisite Information
Now, the fun part.
 * The chart with green, blue, and yellow bars describes the demand for different areas.
 * Different bars of the same color represent different "levels" of buildings. You can check a building's level by pressing on it and counting the number of T signss. Learn more here
 * I will be calling the leftmost green bar G1, the middle green bar G2, the rightmost green bar G3, and all the others in a similar fashion.
 * Green represents residential sections
 * Blue represents commercial sections
 * Yellow represents industrial sections
 * All the experiments took place in medium difficulty
 * In the game, "demand" means potential for growth, or how fast a particular area will grow

The Experiment
When you start a new city, G1 is slightly higher than the others. In other words, only residential areas are in demand, at the beginning.

When I built a 4*4 green area with roads surrounding it, B1 rose. When I build one 4*4 blue area, G2 and Y1 rose. B1and B2 fell. When I built one 4*4 yellow area, G2and B1rose, and Y1and Y2 fell.

When I built a park affecting only the green and a small part of the blue sections, G1, G2, and B1rose.

Adding electric and water systems had no effect on the chart.

Results
So apparently,
 * Adding level 1 residential areas causes the demand for level one commercial areas to grow.
 * Adding level 1 commercial areas causes the demand for level two residential areas and level one industrial areas to grow, and the demand for level 2 commercial areas to fall.
 * Adding level 1 industrial areas causes the demand for level 1 commercial and residential areas to grow, and the demand for level 2 industrial areas to fall.
 * A later experiment showed that parks cause the demand for residential areas level 1 and 2 to grow, regardless of position. They have little to no effect on commercial and industrial areas.