refactor: area value presentation

the areas shown for isochrones is shown as square meters when below
1 square kilometer even if settings are specified to square kilometers as
area units.
As this results in some rather large area values the method is adjusted
to only resort to showing as square meters when below 10000

src/support/geo-utils.js

@@ -192,8 +192,18 @@ const geoUtils = {
    * @param {String} unit
    */
   readableArea(latlngs, unit) {
-    let area = Leaflet.GeometryUtil.geodesicArea(latlngs)
-    return Leaflet.GeometryUtil.readableArea(area, unit)
+    // see https://github.com/Leaflet/Leaflet.draw/blob/33ea262678bbfc3da7e92c226f70c017bd328434/src/ext/GeometryUtil.js#L66-L99
+    let precision = precision || 2
+    let area = this.geodesicArea(latlngs)
+    let areaStr
+    if (area >= 10000 && unit === 'km') {
+      areaStr = Leaflet.GeometryUtil.formattedNumber(area * 0.000001, precision) + ' km²'
+    } else if (area >= 10000 && unit === 'ha') {
+      areaStr = Leaflet.GeometryUtil.formattedNumber(area * 0.0001, precision) + ' ha'
+    } else {
+      areaStr = Leaflet.GeometryUtil.formattedNumber(area, 0) + ' m²'
+    }
+    return areaStr
   },
 
   /**