Traverse That Fails Closure
A surveyor runs a closed traverse around a 40-acre parcel using a total station. The traverse has 8 setups. The surveyor's field notes show angular misclosure of 18 seconds and linear misclosure of 0.42 ft over a total traverse length of 5,280 ft. The relative precision is therefore about 1:12,571. The client's lender requires a survey with a relative precision of at least 1:10,000 for the loan. The surveyor also notes that one backsight was taken on a fence post rather than a monument, and that the temperature was 95°F while the instrument's standard temperature is 68°F. The surveyor did not apply a temperature correction.
1. Evaluate whether the traverse meets the lender's precision requirement and identify the sources of error that should be addressed before finalizing.
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The linear misclosure of 0.42 ft over 5,280 ft gives a relative precision of about 1:12,571, which exceeds the lender's 1:10,000 requirement on its face. However, precision alone does not establish accuracy. The backsight on a fence post is a weak reference and may introduce orientation error; a backsight should be taken on a stable, identified monument or a well-defined point. The temperature difference of 27°F from standard, uncorrected, affects the measured distances; for steel tapes or EDM, the correction should be applied or shown to be negligible. The surveyor should re-evaluate the backsight, apply temperature corrections, and recompute the closure before certifying the survey. If the corrected closure still meets 1:10,000, the survey may proceed; if not, additional field work is needed.
2. The surveyor wants to simply report the 1:12,571 figure and sign the plat. What professional and technical concerns does that raise?
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Reporting a precision figure without correcting known error sources misrepresents the quality of the survey. The fence-post backsight and the uncorrected temperature are known deficiencies that could bias the results even if the closure looks acceptable. Signing the plat certifies the surveyor's professional judgment that the survey meets applicable standards; doing so without addressing known errors is a competence and ethics issue. The surveyor should correct or document the deficiencies, recompute, and only then certify. If the corrected work cannot meet the standard, the surveyor should disclose that to the client and lender rather than paper over it with a favorable-looking ratio.