Principles and Practice of Surveying - Boundary Retracement and PLSS Work for the Idaho Exam
Scope
This domain tests boundary retracement and Public Land Survey System work: recovering corners, deciding which evidence controls, and defending the location you report. Idaho lies almost entirely within the PLSS, so GLO/BLM plats and field notes are the primary record evidence you will be asked to interpret. Expect questions that blend record research with field measurement, where the reasoning path matters more than a formula.
Controlling rules
- Evidence hierarchy: an undisturbed original monument outranks every bearing and distance in the record, and a called-for monument controls a line that is not called for.
- An original corner is never "corrected." A later surveyor who set a corner in the wrong place created a misplaced corner; the original position still governs.
- Obliterated vs. lost: if the position can still be shown from pits, mounds, bearing trees, accessories, or credible testimony, re-establish it there. Only when the position cannot be shown is the corner lost and restored by proportion.
- Single proportionate measurement moves a lost corner along one line between two found controlling corners, applying the record distance to the measured line.
- Double proportionate measurement restores a lost interior corner by proportioning latitude and departure separately, using record distances to the four surrounding found corners.
- Excess and deficiency are distributed by record proportion, never by splitting the difference.
Worked example
Two original corners on a township line are found. Record distance is 80.00 chains; your measurement is 80.40 chains. The 1/4 corner, recorded 40.00 chains from the west corner, is lost. Restore it at (40.00 / 80.00) x 80.40 = 40.20 chains from the west corner. Splitting the 0.40-chain surplus equally would place it at 40.20 only by coincidence on a centered corner, and would fail outright on an offset corner where the record proportion is not one-half.
Traps
Holding the record 40.00 chains as the answer; applying double proportion to a corner on a single line; accepting a distance-only retracement when a monument exists; ignoring accessories that prove an obliterated corner.