Closure error

Closure error, or misclosure, is the gap between where a boundary traverse starts and where its courses actually end when plotted in sequence - a closed boundary should return exactly to its point of beginning. It is expressed as a distance and as a precision ratio (the misclosure divided by the total perimeter, written like 1/15,000).

A small closure error is expected - measurements round, and old descriptions carry the survey methods of their day. A large one usually means a defect in the description or the drafting: a transposed digit, a dropped course, a curve entered with the wrong direction, or a missed table lookup on a plat.

Standards set tolerance in these ratio terms; ALTA/NSPS work is commonly held to 1/10,000 or better. Checking closure per lot, as each shape is plotted, turns closure from a final gate into a live diagnostic that points at the failing call.

Related: Metes and bounds to linework