Blog · September 30, 2026
What Is Double Proportionate Measurement?
Double proportionate measurement restores a lost corner that should agree with record distances in two directions, such as many lost section corners. The corner is placed by comparing north-south and east-west record lengths. It is not a way to center a lot between four fences.
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Two directions at once
A section corner is common to lines that run both ways. If that corner is lost, single proportion along only one mile can satisfy one line and miss the other. Double proportion uses the recovered corners to the north and south, and the recovered corners to the east and west, and it honors the original record distances in both directions. The restored point is the intersection of those two proportioned positions. The method is in the federal survey instructions and in state practice that follows them. It applies to the kind of corner those instructions name. It is not a general recipe for any missing pin in a subdivision.
What has to be true first
The corner has to be lost, meaning the monument and reliable local evidence are gone. The four controlling corners, or the corners the instructions tell the surveyor to hold, have to be identified as the right corners. The record distances come from the original field notes, not from a modern GIS mile. If one of the four corners is itself only a proportioned point, the error can compound, which is why the order of restoration matters and why surveyors restore outward from good evidence. A landowner sketch that uses four fence corners as the controls has substituted occupation for the record. Fences are clues. They are not the four government corners unless a survey shows they were built on those corners.
How to read a plat that used it
A retracement plat should say the corner was lost and restored by double proportion, and it should identify the corners held. Read those sentences before you look at the coordinate. The coordinate is the result. The method and the controls are the reasoning. County tax maps do not run double proportion, and Platbookmapper does not either. The directory links to county GIS so you can open the assessment parcel. It does not restore corners, show zip codes, or import Google lot lines. If the plat is silent and someone tells you the corner was double-proportioned in the field with a handheld GPS, that is not a restoration you can rely on.
What to do next
- Confirm the note says double proportion, not single.
- List the controlling corners in each direction.
- Copy the record distances from the original notes if they are cited.
- Do not apply the method to a platted lot corner.
The mix-up to avoid
Using double proportion on a corner that still has a bearing tree or a stone mound. Local evidence comes first. Proportion is for when that evidence is gone, not for when it is inconvenient.
Questions people ask
Is the restored corner the midpoint of the four miles?
Only if the original record distances were equal in each direction. Double proportion scales the record lengths. Equal modern splits ignore an original survey that chained one side longer than the other.
Can I check the math with a phone?
You can practice the arithmetic on paper. A phone GPS is not accurate enough to occupy the controlling corners, and it is not a survey. Checking a filed plat’s stated method is reading. Re-staking the corner is practice of surveying.
Find the county map
The county GIS map is the practical place to start. Find it from the Platbookmapper directory, then treat the recorded plat and deed as the documents behind the picture.
Not a survey. County GIS and tax parcel maps are assessment and planning layers. They are not a substitute for a recorded plat, deed, or licensed survey.