Ridgeline?

[Narwhalin]

This is a neat way of rigging the tarp. Go to tarp setup: http://www.bushcraftnorthwest.com/articles/articles.htm

I like this way for packing up: http://www.youtube.com/watch?v=DR3DMj-zJu8

The bushcraft article about tarp setup had me thinking...

They use a "ridgeline" running from tree to tree and secure the tarp to that line, then guy out the sides. I thought that you just tied out the tarp to the trees without any line running underneath. Can someone clear this up for me?