Skip to content


Area of Polygon #10

brunosan opened this Issue · 5 comments

3 participants


Add a micro plugin to show the Area of a Polygon when drawing.

This would be useful for e.g. agriculture purposes. Draw a shape and know how many acres that is. (area of a field, lake, ...)

PS: This would need to be projection aware areas. (e.g. currently drawing a circle does not draw a circle on the "ground" -- it does not take into account the distortion due to projection--)

@brunosan brunosan was assigned
Mapbox member

See - would appreciate some tire-kicking of it

Mapbox member

@tmcw nice to flag this. @brunosan if you get this working I could see this being a hot little micro-site that lets us talk to agg folks.


Thanks @tmcw .

Little time spent so far, but I´m going to jump to other things, so posting what I have:

function polygonArea(X, Y, numPoints) 
  area = 0;         // Accumulates area in the loop
  j = numPoints-1;  // The last vertex is the 'previous' one to the first

  for (i=0; i<numPoints; i++)
    { area = area +  (X[j]+X[i]) * (Y[j]-Y[i]); 
      j = i;  //j is previous vertex to i
  return area/2;
map.on('draw:created', function (e) {
        var type = e.layerType,
            layer = e.layer;
            if (type === 'polygon') 
                var area = L.GeometryUtil.geodesicArea(layer.getLatLngs())


  • This seems a planar area (might be ok for now since our first usage is for high res agriculture).
  • Unsure if this covers circumferences. But in such case again restrict to planar, or learn here.
  • Not sure about the units. If pixels, then is just to multiply using the "z-> resolution" chart
Mapbox member

The lower-level area implementation is in - it is geodesic & should correctly handle polygons with holes

@brunosan brunosan closed this
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Something went wrong with that request. Please try again.