The grid of imaginary lines used to locate any point on Earth: latitudes (parallels) measure distance north or south of the Equator, and longitudes (meridians) measure distance east or west of the Prime Meridian.
- Latitudes run east to west and are parallel; they range from 0° (Equator) to 90° north and south (the poles); important parallels are the Tropic of Cancer (23.5 N), Tropic of Capricorn (23.5 S), and the Arctic and Antarctic Circles (66.5).
- Longitudes (meridians) run north to south, converging at the poles; they range from 0° (Prime Meridian, through Greenwich) to 180° east and west.
- The Tropic of Cancer (23.5 N) passes through eight Indian States; India's Standard Meridian is 82.5° East (passing near Mirzapur, Uttar Pradesh), which fixes Indian Standard Time (IST).
- Earth rotates 15° of longitude per hour, so each degree of longitude equals 4 minutes of time; IST is 5 hours 30 minutes ahead of GMT/UTC.
- The International Date Line lies roughly along the 180 degree meridian; crossing it westwards adds a day, eastwards subtracts one.
The standard meridian (82.5 E), IST being GMT plus 5:30, the 1 degree equals 4 minutes rule, and the Tropic of Cancer through India are recurring geography facts.
Latitudes are parallel, but only the Equator is a great circle (parallels shrink poleward); longitudes all meet at the poles. India's standard meridian is 82.5 E, not the Prime Meridian.
Latitudes (north-south position from Equator) and longitudes (east-west from Greenwich); India's standard meridian 82.5 E sets IST.