Each building in the game that is being built on zones has the ability to grow to higher level. Level symbolizes buildings value, wealth of its residents, efficiency and quality of commodities produces and sold there.

If you mark a building from any zone, you will see a bar that symbolizes building level. If you move your cursor above it, you will see a description that will tell you what to do to get the building to higher level.

If it's a residential zone, then buildings there can grow up to level five and have more and more houses per one square meter. Their level mostly depends on education of citizens. Other services have impact on it as well, especially healthcare and safety.

Commercial buildings can grow up to third level. They will mostly want educated workers and high ground value, which means a bit of all services. High level buildings will expect high class resources provided by highly developed industry, so sometimes they will import things from outside the city until you develop your industry to higher levels.

Industrial buildings can reach maximally level three and to do that they mostly need safety and educated workers. Additionally you must provide a bit of each service that increase ground value. More developed industry makes less pollution and produces high class commodities that can be sold in high level shopping centers.

Specialized industry buildings are always on highest possible level.

Offices can also develop to level three. Most important for them is workers education, recreation and ground value.