Canyon Rope Systems
Part of the How Not To video series. This video provides an overview of different ways to set up rappels through a canyon, considering ease of rigging, abrasion, ease of rescue and how efficient it is to move people through the canyon.
Includes a few esoteric systems, the flow chart and some terminology is a bit complicated, but good information nonetheless.
Accompanying webpage includes links to other videos that explain some of the components used: