Why do nine white boxes appear on the screen of iPad flat-panel camera?

The screen of IPAD flat-panel camera shows nine white lines, which is a kind of composition line, called Jiugongge composition. You can cancel it in the camera settings.

Jiugongge composition method is the most common and basic composition method. This composition method divides the left, right, top and bottom of the picture into three equal parts, and then connects the points on the opposite edge lines with straight lines, thus forming a "well" of Chinese characters and dividing the picture into nine squares. Don't put the main body in the middle of the composition, but at the four intersections of the well shape.

The composition lines of Jiugongge can put the subject of photography in the most suitable position, which is helpful to determine the proportion of the sky and the ground, and can also confirm the straightness of lines such as buildings and the horizon to avoid the inclination of composition.