As opposed to the northern/southern hemisphere that has:
- a clear reference point (equators)
- traditionally we don’t model a rotation north/south
Western/eastern hemisphere
- doesn’t have a clear reference (Greenwich?)
- traditionally we model rotation on the north/south axis so western/eastern would depend from the time
Perhaps “clear reference” isn’t the issue. Both the equator and prime meridian are clearly defined.
The equator is kind of a natural landmark, arising from the tilt of the planet. Greenwich is a place built by humans. I think that’s the rub.