There are 10 types of planets which you can colonize in Starpires, each of which helps your empire different ways. Providing credits, growing food, giving your people a place to live, etc. What planet types you decide to colonize is one of the main strategies to building your empire.
Food planets produce the food needed both by your civilian population and troops. You can view your current food productions and empire food requirements on your turn summary. Food production maybe effected by factors pollution and unrest. You can buy and sell food in the global market, but it’s generally much more expensive than it would be for you to grow it yourself.
Urban planets give your population a place to live. Initially urban planets will hold up to 200,000 people, but the closer they are to maximum capacity the slower your population will grow. The more people you have the more tax revenues you bring in. Tax revenues are a great source of income, but it can take longer to build a population base than to build revenues through other means.
Research planets produce research credits that can be used to upgrade or buy new technology under the research tab. They also have other future benefits such as producing chemical and nuclear weapons (once they are researched)
Mining planets most stable of all planets, produce a steady stream of credits regardless of factors like population unrest. They don’t generate as many credits as say a tourism planet, but their stability can be a life saver in hard times.
Supply planets produce military units much cheaper than you can buy them. You can change what types of units they produce with the “Edit” link next to where you buy/sell the planets.
Tourism planets bring in more credits per turn than mining planets, but are heavily effected by civilian unrest. No one wants to visit an empire in civil war. Relying solely on tourism as your empires main source of income is a dangerous strategy.
Anti-pollution planets help keep pollution under control. Will be needed if you have lots of petroleum planets or a high population density. You can view your empires air quality on the right side bar. If your air gets too polluted your population may revolt, your food planets will grow less food, along with other effects.
Government planets help to keep your population in line. Too few of them, and your population can go into unrest quite easily. If you find your populations civilian mood going down, a few more of these might help.
Great schools attract people and will help to grow your population much faster that just relying on new people to be born. If you want to jump start your population growth (particularly early in the game) education planets are a great way to do it.
Petroleum planets can produce the most credits of any planet type, but are affected by supply and demand (the ratio of petroleum planets vs other planets in your empire). They also create a lot of pollution, so if you have a lot of them you will need some anti-pollution planets.