A line joins two points and also divides a space, so it stands both for connection and for a boundary. Drawing one in a dream is read as setting a limit; following one, as keeping to a chosen direction.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.