Appendix H: Map and Compass Skills

Tahoe Backcountry Ski Patrol Manual

Appendix F -- Page 1 of 15 Revised Nov-04 Contents A. How To Use A Map And Compass B. Grid Coordinate Systems 1. Universal Transverse Mercator (UTM) 2. Public Land System (Township And Range, or T&R) 3. Geographic Coordinates (Latitude And Longitude, or Lat/Long) a) Quick and Dirty Method b) Mathematical Method c) Geometrical Method d) Lat/Long Ruler Method C. GPS Uses D. Pratice Problem Answers A. HOW TO USE A MAP AND COMPASS Selecting a compass A good compass with declination adjustment, sighting mirror and clinometer (Suunto MC 2G or Silva Ranger Type 15CL, aka CL515) costs $55-$70. Buy a good one. The following discussion assumes you have followed this advice. Consequently, it does not deal with the procedures and calculations required to correct for declination if your compass does not have a declination adjustment feature. [If you insist on using a compass without declination adjustment, these procedures can be explained in the field, but they are confusing and difficult to remember. Don't say we didn't warn you.] Declination adjustment The Magnetic North Pole lies to the south of true North Pole, which causes an error in compass readings known as declination. The value of declination for a particular area is found on the lower left corner of all USGS maps. For our purposes, declination of 17º east is sufficient for all maps. To adjust your compass, simply insert the small key into the screw on the bottom of your compass and turn the screw until the mark at the rear of the orienting arrow lines up with 17º east declination. Now, unlike those who have compasses without declination adjustment, you will never have to worry about declination again. Map bearings  Mark (or note) your position and destination on the map.  Place the long side of the compass base plate on these two points so that the cover is towards your destination. If necessary, the cover of the compass or a ruler can be used as an extension of the base plate.  Turn the bezel until the meridian lines on the compass capsule are parallel with the meridian lines on the map (or the left or right border of the map) and N on the bezel is on the north side of the capsule with reference to the map.  The bearing from your location to your destination