Land Navigation and Map Reading
Land Navigation and Map Reading tests your ability to use a topographic map and lensatic compass to move and report locations: marginal information, grid coordinates, terrain features, azimuths, declination, pace count, and resection or intersection.
Core rules
- Read map marginal information first: sheet name, scale, contour interval, adjoining sheets, and declination diagram.
- A grid coordinate is read right then up. A six-digit coordinate gives 100-meter precision; an eight-digit coordinate gives 10-meter precision.
- Identify major terrain features by contour pattern: hill, valley, ridge, saddle, depression, spur, draw, cliff, and cut or fill.
- An azimuth is a direction measured clockwise from a reference north. Grid azimuth is measured from grid north; magnetic azimuth is measured from magnetic north.
- Adjust for declination when converting. A common rule: to convert grid azimuth to magnetic azimuth, subtract an easterly declination and add a westerly declination. Reverse the signs when converting magnetic to grid.
- Pace count is the number of steps you take to cover 100 meters on a given terrain and load; it changes with slope, vegetation, and fatigue.
Worked example
Your map gives a grid azimuth of 120 degrees. The declination diagram shows an 8-degree easterly declination. Convert to magnetic: 120 minus 8 equals 112 degrees. Reasoning: easterly declination means magnetic north lies east of grid north, so the magnetic bearing is smaller than the grid bearing. Set 112 degrees on the compass and follow it.
Traps that cost marks
Plotting coordinates up then right instead of right then up; using a magnetic azimuth as though it were a grid azimuth; ignoring declination; and assuming one pace count fits all terrain. Also check that you are using the correct map edition and scale before measuring distance.