Definition of "sightline"

This area, referred to as the fly loft, should typically be two and a half times taller than the proscenium opening in order to fly the scenery above the vertical sightlines of the first row of the audience.

2015, Jeromy Hopgood, Dance Production: Design and Technology, page 44

They drove on, every rise in the road lifting their sightline clear of the drystone dykes along the roadside, gifting glimpses of the firth and the islands, the blue peaks of Arran.

2022, Liam McIlvanney, The Heretic, page 439