How to check a legal description for closure
A metes-and-bounds description should return to its point of beginning. Checking closure tells you whether it does, and by how much it misses.
Latitudes and departures
Each course moves you some distance north or south (its latitude) and some distance east or west (its departure). Working from the course's azimuth, the angle measured clockwise from north:
- Latitude = distance × cos(azimuth), positive to the north
- Departure = distance × sin(azimuth), positive to the east
Add up the latitudes and departures of every boundary course. If the description closes perfectly, both sums are zero. Whatever is left over is the misclosure.
Error of closure
The error of closure is the straight-line distance between where the last course ends and the point of beginning:
error = √(ΣLat² + ΣDep²)
The direction of that error is worth reading too. It is the bearing from the point of beginning to where the traverse actually ended. As the typo guide explains, it often points straight at the bad call.
Precision ratio
A tenth of a foot means one thing on a 300-foot lot and another on a 3-mile boundary, so closure is usually stated as a ratio of perimeter to error:
precision = 1 : (perimeter ÷ error)
A 1,000-foot perimeter that misses by 0.05 feet closes at 1:20,000.
What counts as good closure
A description written from computed coordinates should close very tightly. Rounding bearings to the second and distances to the hundredth of a foot usually leaves a misclosure of a few hundredths of a foot, which works out to 1:50,000 or better on a typical tract. Many offices use 1:10,000 as a working threshold, and some jurisdictions set minimum standards by class of survey, so check the standards that apply where you work.
When the ratio is far worse than rounding can explain, such as 1:2,000 or a misclosure of several feet, the description almost always has a blunder in it rather than a measurement problem.
Ties are not part of closure
Calls from a point of commencement to the point of beginning locate the tract but are not part of its boundary. They should be left out of the closure and area. The checker draws them as dashed lines and excludes them from both.
Checking closure with the checker
- Paste the description, or drop the Word or PDF file, and click Read into table.
- Compare the rows against the original, since text from PDFs in particular can come out with odd spacing.
- Read the error of closure, error bearing, and precision. Set your own threshold in Flag worse than 1: and the result turns red when a tract misses it.