Here is the info from the pinned FAQ:

"Will new content be added to my world I currently are playing on?

New content such as tar pits, mountain caves and Mistlands in the future will not appear in areas that have been already generated. Areas are generated 300-500 meters from a player's location. "Exploremap" and "resetmap" has no effect."

Characters and worlds are separate. You can take existing characters to new worlds, you can create new characters on old worlds, etc. All world changes like buildings or farm patches exist for the new character, but they will have an empty map. Crafting recipes and inventory are tied to the character, regardless of what world they are currently in.

Hope this helps!