Trading and Maintaining Trade Routes
Trade routes are the lifeblood of your civilization, generating Energy that can be used to pay for anything you want. Without them, it's much harder to maintain a profitable economy, but that's not the only thing that they provide. Production, Food, Science, and even Culture are aided by the clever use of trade routes. You can do almost anything with these systems, and it won't cost much to set them up once you know what you're doing.
This chapter explains how to get the most out of trade routes, both internally and internationally.
City Connections
City connections aren't a requirement for trade routes, but they sure help your colony's economy. A City is considered to be connected to your Capital as long as it has a road or magrail that goes all the way to the Capital (passing through other Cities that you control is fine). Cities are also connected if they have access to the same body of water as your Capital and have a clear route scouted between their location and your Capital City.
City connections earn Energy for your colony. This bonus Energy is a rather substantial amount once you connect several Cities. As your Cities grow, they provide more and more Energy per turn for being connected.
Though roads and magrails cost money to maintain, you usually make a profit off of your connections. Don't found Cities that are too far away from your colony, and you won't have to worry much about upkeep. Getting up to Supremacy Level 3 negates upkeep for roads and magrails, so that's another great way to improve the efficiency of your economy.
Even if you can't do much to make your road system cheap, it's worth having one! Movement between your Capital and allied Cities is vital for the defense of your colonies. Taking 15 turns to respond to a buildup of forces along a border is usually disastrous. You want to be able to shuffle units around at will so that each City doesn't have to stand alone. Redistribution of forces enables you to defend your colony with a fraction of the troops that you'd otherwise need to hold off a foe who is willing to scout well and come at you from multiple angles.