Roseway is an area in The Outer Worlds that you will have to travel to fairly early on in the main game, but it's not all that obvious exactly how you get there.
You can get to Rosewater after your finish the first mission with Edgewater in the Deserters area on Terra-2. At this point you will head off to the Groundbreaker, and you should talk with Gladys once you are there.
She will offer you the navkey to Roseway if you either pay her 10,000 Bits (which is a lot of Bits at this point in the game), or complete a short quest for her. She wants you to investigate a distress signal from Roseway, so follow this quest marker to get the distress signal item. When you have that, head back to the Unreliable and talk to ADA. At this point you will unlock the ability to travel to Roseway.
To travel to Roseway, go to the planet menu and select Terra-2. Now you have two options here; Edgewater or Roseway. Simply click on Roseway to travel there, and you will land in this new area.