The Yosemite Decimal System (YDS) is a rating system used by rock climbers to choose appropriate climbs that are challenging, within their abilities, and to bring proper gear. There are many factors which influence the ratings, such as the difficulty, time commitment, length of climb, and risk. Although YDS is mostly used in the United States, YDS classes are mapped to other national and regional climbing rating systems.
YDS was leveraged to chart existing LCSH terms to the different YDS classes.
|YDS Class||Definition from Appendix A in Mountaineering: The Freedom of the Hills||Library of Congress Subject Headings||Keywords||Title or Description|
|Class 1||Hiking.||Hiking||-||Hiking or hiker|
|Class 2*||Simple scrambling, with possible occasional use of the hands.||Hiking||Scrambling||Scrambling|
|Class 3*||Scrambling; hands are used for balance, a rope might be carried.||Rock climbing||Scrambling||Scrambling|
|Class 4||Simple climbing, often with exposure. A rope is often used. A fall could be fatal. Typically natural protection can be easily found.||Rock Climbing||Scrambling||Scrambling|
|Class 5||Where rock climbing begins in earnest. Climbing involves the use of a rope, belaying, and protection (natural or artificial) to protect the leader from a long fall.||Rock climbing||-||Rock climbing or rock climbers|
|5.0-5.7||Easy for experienced climbers; where most novices begin.||Rock climbing||-||Rock climbing|
|5.8-5.9||Where most weekend climbers become comfortable; employs specific skills of rock climbing, such as jamming, liebacks and mantels.||Rock climbing||-||Rock climbing|
|5.10-5.11||A committed recreational climber can reach this level||Rock climbing||-||Rock climbing|
|5.12-5.15||The realm of true experts; demands much training and natural ability, as well as, often repeated working of a route.||Rock climbing||-||Rock climbing|
* If LCSH changes “Alpine scrambling” to Scrambling, then “Scrambling” should be added as a Subject Term to these Classes.