Link 1: MAPfrappe - Move Outlines

MAPfrappe is a Google Maps mashup that lets anyone outline an area on one Google Map, and compare that area on another Google Map. Outlines can be saved.
Link 2: MAPfrappe: Index of Outlines

United Kingdom and Ireland compared to South Africa:

Compare other features: Parks, Buildings etc:

Kensington Gardens, Hyde Park and St James Park vs central Park:

Or trace and save your own outlines.