formatArea = function (polygon) {
  const area = getArea(polygon);
  let output;
  if (area > 10000) {
    output = Math.round((area / 1000000) * 100) / 100 + ' ' + 'km<sup>2</sup>';
  } else {
    output = Math.round(area * 100) / 100 + ' ' + 'm<sup>2</sup>';
  }
  return output;
}
Format area output.
@param {Polygon} polygon The polygon.
@return {string} Formatted area.