Reference line
WARNING: This page is about a different car, the 2017 Honda Odyssey, 2016 Honda Odyssey, 2015 Honda Odyssey, and 2014 Honda Odyssey. However, it is still accessible from the selected car via links, so may be relevant.
The LaneWatch image is provided with the three reference lines, each line shows the distance from the rear bumper. Three lines that appear on the center display can give an idea of how far the vehicles or objects on the center display are from your vehicle, respectively. If an object is near line 1 (in red), it indicates that it is close to your vehicle whereas an object near line 3 farther away.