ogleearth - So what does this center of gravity calculator do, precisely?
Practically speaking, the spot you get back minimizes the total distance (among points) people at placemarks will need to travel in order to meet up together. And if you calculate the center of gravity for just two placemarks, the straight line you can draw through all three points will be the shortest distance as the jumbo jet flies between your two placemarks.
Mathematically speaking, the code first finds the center of gravity for given points of equal mass on the surface of a sphere in three dimensional space. (The center of gravity will thus be inside the sphere.) It then finds the point on the sphere closest to the center of gravity by projecting a straight line from the center of the sphere through the center of gravity to the surface of the sphere. cool.
The algorithm assumes Earth is a sphere, even though it is actually a geoid, so errors of tens of meters will persist. Correcting for those is something I am two PhDs short of being able to do.

The original story is three posts down, here:
Blogger "Brammeleman" writes in Dutch (so I'll translate loosely) that his family is discussing where to have the next family reunion. It must be a nerdy family, as everyone immediately agreed it should be at the family's center of gravity. The only question remaining is, what determines the weighting of each individual family member?While the rest of the family argues it out (age? generation? marital status?), our blogger has gone off and produced a center of gravity calculator for Google Earth. In the true political tradition of the Dutch, the calculator assigns everyone an equal weighting.
... I tried it. My immediate family is all over the place — London, Switzerland and me here in Stockholm, yet the center of gravity for us is in tiny Belgium. As we're Belgian, that's rather spooky.

Neat "center of gravity" calculator for Google Earth. following on Cory's map of the center of gravity of Manhattan's Starbucks. #