When establishing a trade route, the user interface lists destinations that are reachable from the current origin city. A trade route must be completely explored (i.e. have no fog of war to cover it) and must not have any Miasma on it (unless you have 2 Harmony points). Aside from those restrictions, there are no limitations on the length of a trade route. In the trade route screen you will see that all potential destinations have little arrows below them listing the resources that the route would generate. The File:Left arrow (CivBE).png left arrow means imports and the File:Right arrow (CivBE).png right arrow means exports. In other words, File:Left arrow (CivBE).png left is what the origin city would receive, while File:Right arrow (CivBE).png right is what the destination city would re