Some useful tips to draw lines on sloped terrain
In this useful sketchup video tutorial, one will learn how to apply sketchup for adding lines to a 3d sloped terrain.
Go to view in geometry and there will be a bundle of triangulated faces which form the mesh. While going to draw on terrain or any curved object, ensure that hidden is turned on in order that it is possible to join lines at a face.
Every face should be flat, so any two edges which are drawn on that line will facilitate to form that shape.
To watch the complete tutorial, go through the following video.
Video Source Designer Hacks