That's great!
There's the new relationship between City and Flight.
Remember that we did not have to decide before we drew it just how the
relationship would flow. First we draw; then we define.
Many data modeling tools have different tools for each form of relationship - one-to-one, one-to-many, many-to-many, etc. They require you to model the relationship in your head before you choose the tool to model it on the screen.
PowerDesigner allows you to note your ideas as quickly as they pop into your mind and go back at any time to refine them.