An imaginary line is a term used to describe an invisible boundary or demarcation that separates two things, such as countries, states, or territories. Full definition
In their attempt to prove their theory they draw imaginary lines connecting the dots the way they want them to appear. (religion.blogs.cnn.com)
There is some sort of imaginary line that is drawn, and everybody on one side of the line is «good with God,» and everybody on the other side needs to «get right with God.» (redeeminggod.com)
There's been a lot worse shown on the show, so let's all just calm down and stop drawing imaginary lines in daft places. (wolfsgamingblog.com)