Field Survey Procedures, Measurement Analysis and Monumentation
Field Survey Procedures
Before the field
Field work begins with record research - deeds, subdivision maps, GLO notes, corner records - followed by reconnaissance. Calibrate instruments, verify prism and EDM constants, record the datum and epoch for GNSS, and check control by tying to at least two independent monuments or published control points. California law (Business and Professions Code) governs monument preservation: do not disturb an existing monument without authorization, and file a corner record when one is required. Call 811 (Underground Service Alert) at least two working days before digging.
In the field
Establish control first, then traverse or use network RTK with independent checks. Close traverses and compare redundant observations. Record monument type, cap markings, condition, and ties; photograph the site. Field notes should be legible, original, and complete enough for another surveyor to reproduce the work without guessing.
Traps
- Skipping record research, or 'finding' only what fits a preconceived line.
- Accepting GNSS positions without checking datum, epoch, scale, or local control.
- Setting monuments that are too shallow, unstable, uncapped, or missing the license number.
- Failing to tie accessories - bearing trees, witness corners, fences - that may be the only surviving evidence later.
- Omitting the reason a monument was accepted or rejected.
Worked example
A retracement traverse closes 1:12,000. That is precision, not accuracy: a systematic prism-constant error can produce a perfect closure while shifting every point. Check against an independent tie to a found monument or published control before accepting the traverse.
Rule of thumb
Observe more than you need, and document more than you observed - the next surveyor inherits only what you wrote down.
Measurement Analysis and Monumentation
Error analysis
Measurements contain random, systematic, and gross errors. Random errors tend to average out and are described by standard deviations. Systematic errors - prism constant, atmospheric correction, scale factor, level collimation - shift everything in the same direction and do not average out. Blunders are mistakes. A least-squares adjustment minimizes the weighted sum of squared residuals, with weights inversely proportional to variance; redundancy allows blunder detection and estimation of the reference variance.
Interpreting results
Residuals are the corrections applied to observations. An error ellipse at a stated confidence level (commonly 95 percent) describes positional uncertainty, and a long semi-major axis signals weak geometry. Precision is repeatability; accuracy is closeness to truth. A tight closure does not prove accuracy, and coordinate values are not evidence of boundary location.
Monumentation
Set monuments that are durable, stable, identifiable, and consistent with the map or record - rebar with a cap stamped with the license number, concrete monuments, or brass disks - set below the mower line, tied to accessories, and documented with a corner record where required.
Traps
- Treating a good closure as proof of accuracy.
- Mixing standard deviations with confidence regions, or running unweighted adjustments.
- Setting a monument that does not match the description on the map.
- Ignoring a reference variance far from 1.0, which signals wrong weights or a systematic error.
Worked example
A least-squares adjustment yields residuals near 0.02 ft with a reference variance near 1.0, consistent with the assumed weights. A reference variance near 9.0 suggests the weights were optimistic or a systematic error remains.
Rule of thumb
Check the reference variance and the error ellipse before you trust the coordinates - geometry beats computation.