Why is 0 degree longitude and 180 are not designated east or west?

Answer 1

Simply because it doesn't matter in either case.

-- Zero east or zero west puts you on the Prime Meridian either way.

(Beginning on the Prime Meridian, you may travel 0° east or 0° west,

as you prefer, and you arrive at the same place either way.)

-- 180° is half-way around any sphere. Regardless of which direction you decide

to travel from the Prime Meridian, 180° east or 180° west puts you exactly half-

way around the Earth, in the same place.

Answer 2

Because those are the ones that were left up to your pleaseure. Where the

longitude of a place is zero, you're free to call it zero east or zero west, as you

wish. And if the longitude of a place is 180, you may call it 180 east or 180 west,

as it pleases you. Similarly, if the latitude of a place is zero, you may call it zero

north or zero south. You'll be fastidiously and precisely correct eaither way, and

nobody will argue with you.

Answer 3

Simply because it doesn't matter in either case.

-- Zero east or zero west puts you on the Prime Meridian either way.

(Beginning on the Prime Meridian, you may travel 0° east or 0° west,

as you prefer, and you arrive at the same place either way.)

-- 180° is half-way around any sphere. Regardless of which direction you decide

to travel from the Prime Meridian, 180° east or 180° west puts you exactly half-

way around the Earth, in the same place.

Answer 4

0 degree longitude is designated as the Prime Meridian since it is the starting point for measuring longitude. It divides the Earth into Eastern and Western Hemispheres. 180 degrees longitude, on the other hand, is the International Date Line, where the date changes when crossed from east to west.