I think (I'm not sure, I didn't get to watch them string it up) that the lines are long enough they can anchor it on one side, and then "walk" it around (hence why it worked well to put it in a horseshoe shaped canyon rather than across). I got to see it up close -- the complexity of the anchors was pretty amazing. This required several climbers, etc. to consolidate/contribute gear. I've also seen things more complicated going from a cliff to a spire - I presume they climb with a guide rope and haul the other end up? Most of the people setting this up are pretty famous/accomplished climbers.

I had a chance to go out to the "space net" - you wear a harness and slide out on the support lines if you're not comfortable walking the lines. I was mainly afraid I'd not be able to pull myself up on the net once I got there (I really lack upper body strength) and the thought of two or three people trying to haul me over the edge just wasn't my cup of tea. Maybe next year (they've had a similar setup two years in a row and I'm sure they'll have it again next Thanksgiving).