Have you ever thought where you would end up if you drilled a tunnel through the center of the Earth and climbed out the other side? Well that location is considered an antipodal point. The antipodes of any place on a globe is the point on the surface which is diametrically opposite to it. Two points that are antipodal to each other are connected by a straight line connecting through the center.
Mathematically, the geographical coordinates of an antipodal point can be calculate as: the latitude of the place you want to find the antipodes must be converted to the opposite hemisphere (eg: 45° North will be 45° South or -45°); the longitude of the place you want to find the antipodes must be subtracted from 180° and the result will be converted to opposite hemisphere (eg: 25° West will be 180° – 25° = 155° East or -155°).
The majority of locations on land do not have land-based antipodes.
In 2013 I wrote an article for GoGeomatics magazine about an interactive maps that revealed what the Antipodes for any given location was. It has turned out to be one of the busiest articles in the magazine, attracting a lot of attention, perhaps because many geomatics people have not taken many geography courses.
The site that I was referencing to in the article seemed to have disappeared some time last winter, therefore no one could use the interactive antipodes calculator. Well now the site is once again active and people can once again learn a little bit of geography in a funny and simple way.
So check out http://www.antipodesmap.com to have a little fun exploring their interactive antipode calculator map.