Honda TRX500FA 2006 Owner's Manual page 58

Longitudes, also called meridians, are vertical circles extended from the
North Pole to the South Pole. The zero degree longitude, which passes
through Greenwich, England, divides the Earth into the Eastern and
Western hemispheres. The 180 degree longitude, half way around the
planet, is the international date line.
LONGITUDE
0° longitude
(Greenwich,England)
Western
Hemisphere
Each longitude 69 miles wide
Each time zone equals 15° longitude
North Pole
South Pole
Introduction
180° longitude
(international date line)
Eastern
Hemisphere
GPScape System
49