Greenwich wasn't arbitrary at all.

http://en.wikipedia.org/wiki/International_Meridian_Conferen...

Historical precedent and agreement make the choice no less arbitrary - 0 degrees could have been anywhere, there is no technical reason that Greenwich was chosen.

It says so right in the article.

Choosing Greenwich as 0-longitude meant that the International Date Line would be located in the middle of the Pacific Ocean, avoiding a situation where it could be two dates in the same country simultaneously.

Have you looked at the map for the IDL?

http://upload.wikimedia.org/wikipedia/commons/6/61/Internati...

That not jiggered by politics at all.

I thought we were talking about the "arbitrary" choice of Longitude 0. What's the political (and not economic) basis for the later IDL modifications?

That fails to make the first choice any less arbitrary - the choice was made to line up with existing sea charts - which of course used the Greenwich as 0 - but Greenwich as 0 was an arbitrary choice in the first place - not all arbitrary choices are bad ones, that was the crux of my argument in the first place.