Air traffic controllers direct commercial flights to fly at “even” or “odd” altitude levels. The general rule in most parts of the world is aircraft going East will fly at odd levels, i.e. 35,000 ft., while aircraft heading West will fly even levels, i.e. 34,000 ft. – WTF Fun Facts
Source: Up in the Air: Who Determines a Plane’s Altitude? (thepointsguy.com)
Much appreciated G. B.! I learned something new.
North is considered east (everything from 0° to 179°) likewise south included with west altitudes (from 180° to 359°)
What about North and south?