GPS Polygon Area Calculator

Each corner carries 3–5 m of error (single-frequency consumer GPS in open sky), and area error scales with perimeter × point error: a square 1-ha plot (400 m perimeter) lands within roughly ±3–5%; a 10-ha plot within ~1–2%; a 100-ha farm well under 1%. Small urban plots fare worst — multipath off buildings can push corner errors to 10+ m, swamping a 200 m² yard. Improve it: average 30 s per corner, log in open sky, use a dual-frequency phone (increasingly common) — or rent an RTK receiver for centimetre truth.

Sequence matters, direction doesn't: enter the corners as you'd walk the boundary — clockwise or counterclockwise both work (the formula's sign is absolute-valued away). What breaks the math is zigzagging across the parcel: the shoelace formula interprets the list as the boundary path, so a crossed ('bow-tie') sequence partially cancels its own area. If the result looks absurdly small, that's the signature — re-order the points to follow the fence line.

No — and the gap is institutional, not mathematical: legal boundaries are defined by deeds, monuments and licensed surveys on official datums, with court standing. GPS-walked areas serve everything one step short of that: sanity-checking a parcel before purchase ('the listing says 2 acres; I measure 1.6'), fertilizer and seed-rate planning, irrigation design, lease negotiations, crop-insurance estimates and farm recordkeeping. Surveyors' RTK gear measures the same way — with centimetre receivers and legal authority.

A genuinely multi-cause mystery: historic surveys used chains and offsets with their own errors; deeds sometimes record SLOPE area on hilly land (this tool computes horizontal/map area — a 20° hillside's surface is 6% bigger than its footprint); boundaries drift as fences get rebuilt off-line; units mutate (local bighas and guntas vary by district — our land-unit converter handles those); and occasionally the record is simply wrong. When the discrepancy matters, the sequence is: re-walk with better GPS, then compare against cadastral maps, then hire the surveyor.