ALTA/NSPS relative positional precision

The allowable relative positional precision between two adjacent boundary corners under the 2026 / standards, compared with the 95% error ellipse from your adjustment.

Experimental: not yet fully verified. How results are checked

Computing your own values needs JavaScript and WebAssembly. The worked example below was computed when this page was built, and the documentation under "How we got this" applies.

0.12ft

The standard allows 0.12 ft between these corners.

Within your 0.12 ft allowable RPP (ALTA/NSPS 2026) Against Minimum Standard Detail Requirements for ALTA/NSPS Land Title Surveys.

Your 95% semi-major axis

Provenance

Computed by: survey.land.alta-rpp 1.0.0, core 0.1.0
Model: Allowable = 2 cm (0.07 ft when the distance is in feet) + 50 × 10⁻⁶ × distance (ALTA/NSPS 2026, 3.E.v). RPP is the semi-major axis of the 95% error ellipse of the line between the corners: 2.448 × √(largest eigenvalue of the east-north covariance) when a covariance is given
Accuracy: The allowable value is exact; the comparison is as good as the adjustment's weighting. Misclosure is not RPP and is refused
Notes: 1 shown with the answer
Cites: American Land Title Association and National Society of Professional Surveyors, Minimum Standard Detail Requirements for ALTA/NSPS Land Title Surveys

Something look off?

Your values

Showing an example. Change anything.

Distance between the corners Direct, like 1000 ft · plain numbers mean ft 95% ellipse semi-major axisoptional Of the line between the corners, from the adjustment, like 0.05 ft · plain numbers mean ft σ of the east differenceoptional Or give the covariance, like 0.02 ft · plain numbers mean ft σ of the north differenceoptional Like 0.015 ft · plain numbers mean ft

More options 2

East-north covarianceoptional In square feet, like 0.0001 (the default 0) Traverse misclosureoptional Like 0.05 ft. Not a measure of RPP; the tool explains why · plain numbers mean ft

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How we got thisFormula, worked example, sources, and proof

Model: Allowable = 2 cm (0.07 ft when the distance is in feet) + 50 × 10⁻⁶ × distance (ALTA/NSPS 2026, 3.E.v). RPP is the semi-major axis of the 95% error ellipse of the line between the corners: 2.448 × √(largest eigenvalue of the east-north covariance) when a covariance is given

Show your work

Distance term
50 × 10⁻⁶ × distance
50 × 10⁻⁶ × 1,000 = 0.05 ft
Allowable RPP
0.07 ft + distance term
0.07 + 0.05 = 0.12 ft

The same steps an agent gets from the MCP server with explain: true.

Accuracy: The allowable value is exact; the comparison is as good as the adjustment's weighting. Misclosure is not RPP and is refused

Worked example: Adjacent corners 1,000 ft apart, a 0.05 ft ellipse. Source: add-practitioner-essentials RPP scenario: 0.12 ft allowable at 1,000 ft. It is golden test vector v001, and every build checks the tool still gives its answer within its tolerance.

You enter

Distance between the corners: 1000 ft
95% ellipse semi-major axis: 0.05 ft

You get

Allowable RPP: 0.12 ft
Your 95% semi-major axis: 0.05 ft
Against the standard: Within your 0.12 ft allowable RPP (ALTA/NSPS 2026)

Review: Not yet independently reviewed by a licensed surveyor.

Last verified: 2026-09-22, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.0.0, core 0.1.0. See this tool in the verification report.

Checked against: 5 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

Minimum Standard Detail Requirements for ALTA/NSPS Land Title Surveys, American Land Title Association and National Society of Professional Surveyors, 2026 standards, effective February 23, 2026. Section 3.E.i (Relative Positional Precision: the semi-major axis of the 95% error ellipse between adjacent corners) and 3.E.v (at most 2 cm (0.07 feet) plus 50 ppm). Rules as of 2026-09-22.

Terms

ALTA: American Land Title Association: The title insurers' association that, with NSPS, sets the standards for land title surveys. Source: Minimum Standard Detail Requirements for ALTA/NSPS Land Title Surveys
NSPS: National Society of Professional Surveyors: The US surveyors' society that, with ALTA, sets the standards for land title surveys. Source: Minimum Standard Detail Requirements for ALTA/NSPS Land Title Surveys
RPP: relative positional precision: How well two adjacent boundary corners are located relative to each other: the long axis of their 95% error ellipse. Source: Minimum Standard Detail Requirements for ALTA/NSPS Land Title Surveys

Experimental means this tool has not yet met the stable bar: at least 20 golden vectors, differential tests, and an independent worked example.

ALTA — American Land Title Association

The title insurers' association that, with NSPS, sets the standards for land title surveys.

Source: Minimum Standard Detail Requirements for ALTA/NSPS Land Title Surveys

NSPS — National Society of Professional Surveyors

The US surveyors' society that, with ALTA, sets the standards for land title surveys.