When is a resection used in land navigation?

• A. To determine one's own position on a map by determining the grid azimuths of two well-defined locations
• B. To determine the grid azimuth of three locations to locate oneself
• C. To estimate speed by map scale
• D. To measure distance to a known landmark

Answer: (A)

Resection is a position-finding method that uses known landmarks and their grid directions to locate yourself on a map. You sight two well-defined features you can identify on the map and determine the grid azimuth from your position to each feature (or from each feature to you). On the map, you then draw a line from each landmark along its azimuth. The point where those two lines intersect is your location on the map. This is why using two landmarks to get two grid azimuths is the standard description of how resection works. Using three landmarks is another variant that can increase accuracy, but the basic concept centers on two lines of position intersecting to fix your location. The other options describe different techniques: estimating speed from map scale and measuring distance to a landmark are not resection.