MAPfrappe.com allows anyone to outline an area on Google Maps, and then compare that area elsewhere on the Earth.
MAPfrappe compensates for these effects. The results of moving an outline around the map can sometimes be surprising.
For example:
Try it out, or view a previously created outline:
The above Google spreadsheet is publicly shared. Anyone can edit it. Create an outline on MAPfrappe, make a url, and add it to the spreadsheet at Google Documents: MAPfrappe Index.
More examples: