This Google Mapplet can be used to measure polygonal area and perimeter on a sphere in Google Maps using an open source library GeographicLib. Using the mapplet is easy - simply place click three or more points on the Google Maps backdrop to define a polygon; the area and perimeter values will be displayed in the centroid of the polygon.
The default units of measurement for area and perimeter, as well as the polygon boundary color can be changed by selecting the desired values in the right pane.
Once the measurement polygon has been placed on the map backdrop, the vertices can be adjusted either by manually dragging a vertex marker with the mouse or by clicking the vertex marker and entering refined latitude and longitude values.
A vertex marker can be deleted by clicking on the vertex marker and selecting the Delete option.
The mapplet can be found at this link http://dominoc925-pages.appspot.com/mapplets/geoarea.html.