Trade represents income generated by ships equipped with trade modules, such as Freighters. In order to establish a trade route, a trade module equipped ship must move to a planet belonging to another civilization. The value of the trade route is proportional to the length of the route, as well as the population of both the destination and home planet of the trade ship. Once the trade ship reaches the destination planet, the trade route will be established (represented by a faint trail on the main map). The income returned each turn by the route is proportional to the distance of the trade ship from the home planet. Trade ships are able to be attacked, so they should either be protected or only allowed to operate in safe areas of space. Civilizations can only have a limited number of trade routes, a number that can be affected by technology, racial bonuses, and United Planets votes. The trade tab of the Domestic Policy screen lists your civilization's current trade routes as well as their average income. This is also where the maximum number of trade routes for your civilization can be found. This screen can be used to discontinue trade routes if necessary.