map Measure Land Area on a Map star

How the Area Is Calculated

Every corner you click becomes a vertex of a polygon, and the tool applies the Shoelace Formula (also known as Gauss's area formula): Area = ½ × |Σ(xᵢ × yᵢ₊₁ − xᵢ₊₁ × yᵢ)|, summed around all vertices in order. The formula works for any simple polygon — three corners or thirty, a perfect rectangle or a wildly irregular shape following a stream bank — as long as the corners are entered in a consistent order (clockwise or counter-clockwise) and the boundary does not cross itself. Corner count and shape do not matter to the math; only the coordinates do.

Worked example: a four-corner parcel converted to local meters at (0,0), (60,0), (65,40) and (5,45). Applying the formula: ½|(0×0−60×0) + (60×40−65×0) + (65×45−5×40) + (5×0−0×45)| = ½|0 + 2400 + 2725 + 0| = 2,562.5 m² — about 2.56 dunams / 0.256 hectares. Add a fifth corner mid-boundary and the same formula recalculates instantly; there is no need to pick a "shape type" first.

What to Know

The formula itself is exact — the real source of error is how precisely each corner was clicked or recorded. Consumer GPS and satellite-imagery clicks typically carry ±3-5 meters of positional error. On a large parcel that is negligible, but on a small plot the same absolute error becomes a much bigger relative one: a 5 m error on a corner of a 2-hectare field barely moves the total, but on a 200 m² garden plot it can shift the area by 10% or more.

• Always click corners in one consistent rotational order — mixing directions on the same polygon can make the formula miscount the area.
• Satellite imagery is commonly offset several meters from official cadastral coordinates — treat this tool as a planning/estimation aid, not a legal survey.
• For deed disputes, subsidy applications or sale contracts, an official cadastral/land registry record is the authoritative source.

A quick sanity check: click the same corner twice from different zoom levels and compare the two — if they land more than a few meters apart on screen, the map or zoom level needs adjusting before the polygon can be trusted. Consumer smartphone GPS is far less precise than the survey-grade GNSS receivers licensed surveyors carry, which is exactly why casual map measurements and official cadastral figures are expected to diverge by a small but non-zero margin, and why the two numbers serve different purposes: one for planning a purchase or fence, the other for settling a legal boundary.