There are three facets to growing your city: People, Money and Pollution.
People are gained by building more houses. These houses can then perform Eco Actions, which eliminate the pollution already produced. However, these people constantly produce more pollution. You can unlock upgrades, which will eventually eliminate this pollution. Without these upgrades, you would be fighting a losing battle against mounting pollution. Homes, upgrades and everything else costs money. You gain money from economic activity, represented by shopping centres and office buildings. These buildings slowly accumulate money, which you can collect when you want. However, since activity always causes pollution, there is a cost to this money in the form of additional pollution. Eventually you can build upgrades and facilities to mitigate this pollution as well. All this pollution ends up in three repositories, represented in the game by the Power Plant, Sewage Pipe and City Dump. Your ultimate goal will be to clean up all the pollution stored here, at which point you will attain the ultimate reward.
Homes come in three types. They house a different amount of people and produce different amounts of pollution. However, each house is equally effective in doing Eco Actions.
Offices provide a place of employment for your workforce. Offices generate money based on how many workers there are. Offices can be upgraded like houses to eliminate the pollution caused by money production. You should strive to a balance between homes and offices.
Shopping centres generate money based on how many people shop there. You cannot build upgrades to shopping centres, instead you must build separate facilities such as solar plants, sewage treatment plants and various factories to counteract the pollution produced.
The first step in removing solid waste is sorting it. However, that sorted waste must have some end destination or it will still end up at the city dump. This is where the various production facilities come in. Once a production facility is set up it will reduce the waste output of homes. Since the finished goods are then sold at the shopping centres, they also reduce the waste generated by shopping centres by an equal amount.
Generated pollution is stored in infrastructure buildings: Power Plant for CO2, Sewage Pipe for sewage and City Dump for waste. From their info screens you can see how much pollution remains, how much is added daily, and what the overall mitigation rate is.
Keeping track of pollution
As an upgrade is built, it reduces the pollution that the building generates. This is called mitigation and is expressed in the game as a percentage next to a recycling symbol. You can check individual mitigation percentages and remaining pollution output in the info screens of various buildings. The information for shopping centres takes into account the effect of solar plants, sewage treatment plants and factories. You can check overall mitigation and pollution production at the Power Plant, Sewage Pipe and City Dump.
In the top right corner is a score indicating your overall success in managing your town. It is affected by your population level and the overall mitigation of pollution. Tapping the display opens a breakdown of the various factors affecting your score.