Using the site antipodesmap one can quickly explore what the opposite point of the earth to any location would be. That is, the surface point connected to this point by a straight line through the centre of the earth.
It is easy to see that most land points have antipodes which lie somewhere in water, which made me wonder:
How much land area (as a fraction of total land area) has antipodal land area?
And how would I best find this out? Can somebody produce a map of those areas, e.g. highlight those areas on a world map?