This Google Maps lets you see an outline of one part of the world overlayed on top of another part of the world. For example, you can sketch an outline of California and then overlay the outline over Japan.
In the example in the screenshot above I've overlayed an outline of the UK on the United States. MAPfrappe comes with a number of preconfigured examples, overlaying the outlines of countries on top of other countries and landmarks on top of other landmarks. For example, here is a comparison of London's Hyde Park and Green Park with New York's Central Park,