Chapter 5: Mobile Mapping Fundamentals

Nicolas MalloyAuthor: Nicolas R. Malloy


5.10 Resection


Out in the field you can use a USGS topographic quadrangle and a compass to find your position using a method called resection. This technique involves plotting lines that cross your position.

Observing your surroundings, locate two or three landmarks that you can identify on your map. Using the compass, you can acquire the azimuth of each landmark relative to your position. Calculate a back-site, or back azimuth, for each landmark and set this value on the compass using the bezel and the index pointer.

You can orient the compass on the map along the back azimuth using the meridian lines. Once the meridian lines on the compass align with the meridians on the map, draw a line from your landmark back towards your position using the compass as a straight edge. Repeat this process for each landmark. Your position will be located where all of the lines cross.

Tip Of The Week – “Resection” – How To Determine Your Location With A Map And Compass (E9) by IntenseAngler

You can also locate the position of a distant landmark or object using an opposite method called intersection. The intersection method uses a series of foresights, or azimuths, taken from two or more positions. Using the compass, you can acquire the azimuth to the target at your current position. Moving to a second and third position, you can acquire additional azimuths to the target. Once you record each azimuth, plot the lines on a map the same way used for the resection method. The place where all the lines cross is the position of your landmark or object.

Intersection and Resection by RangerKSchool