You can also go to the planet screen and select the planet to trade with there. The quickest way to set up a trade route or a harvesting route is go to the planet listing screen and select a planet from there. You don't have to navigate through all the maps to find your planet.

If you select a planet in he planet listing you will see that you can set the route to that specific planet.

Although showing which ones you are trading with might be something we need to look at adding.