Upvote:1
That line vaguely details the original elevation of the hill upon which the Great Pyramid rests. There are theories that the original hill which used to hold the Sacred Well, whose remains are part of the Grotto, was terraced in order for the Pyramid to rest flat on the plateau. This same terraced hillside is shown in many plan views of the Pyramid, including the one below.
Upvote:9
It is a shadow to show the vertical displacement of the Grand Gallery.