Land area and distances measured on a map
An online tool for measuring land area and distances on a map: trace the boundary with points and the area is computed on the WGS84 ellipsoid, in hectares, ares or acres. It also shows what a tool measuring the on-screen picture would have claimed — at Moscow’s latitude, about three times too much.
How to use it
Pan the map to the plot, or press “My location”. Tracing boundaries is easier on the satellite layer, which is in the top right corner of the map.
Click each corner. The area appears from the third point; for a route or a fence along a road, switch to Distance mode.
Drag a point that landed badly and the numbers update immediately. Clicking a point removes it; “Undo point” drops the last one.
Ares for a garden plot, hectares for a field, acres for English-language paperwork. Length switches separately.
“Link to this measurement” puts the outline in the page address; GeoJSON and KML download a file for GIS or Google Earth.
Trace a plot and get the area a surveyor would calculate
Click the map to drop points. Drag a point to move it, click it to delete it. The satellite layer is in the top right corner.
How this is computed
Distances use Vincenty’s formula on the WGS84 ellipsoid — the surveyor’s standard, accurate to millimetres. The spherical formula most sites use is off by up to half a percent: 16 kilometres on Paris–New York. Area is integrated over the authalic latitude rather than measured on screen: Web Mercator stretches shapes more the further you go from the equator, and at Moscow’s latitude the area error is about threefold. Verified against published figures: a 1°×1° cell at the equator, the area of Colorado, the full surface of WGS84, and a 100 × 100 m square that must come out as exactly one hectare.
