Latitude is angular distance north or south of the Equator, measured up to 90°. The Equator is 0° latitude; the poles are at 90° north and south.

Longitude is angular distance east or west of the Prime Meridian, measured up to 180°. Meridians meet at the poles; parallels of latitude form circles that become smaller towards the poles.

A coordinate pair identifies location. Latitude strongly relates to solar-angle patterns, while longitude is used to compare local times.

Earth rotates approximately 360° in 24 hours, corresponding to 15° per hour or four minutes per degree of longitude for local solar-time comparison.

Places to the east are ahead in local solar time. A place 30° east of another is about two hours ahead, before considering time-zone conventions.

Indian Standard Time uses the standard meridian of 82°30′ E and is UTC +5:30. A national standard time is a convention; it is not every location’s exact local solar time.

If the local solar time at 60° E is 12:00 noon, find the local solar time at 75° E. Difference = 15°. Time difference = 15 × 4 minutes = 60 minutes.

75° E lies east of 60° E, so its time is ahead: 1:00 pm. Always decide east or west before adding or subtracting.

For international travel and calendar dates, use the actual time zone and date-line convention, not only a longitude calculation.

Latitude is angular distance north or south of the equator, measured up to ninety degrees. Longitude locates an east–west position relative to the prime meridian and is measured up to 180 degrees east or west. A coordinate pair identifies a position; neither coordinate alone usually fixes one point. Lines of latitude are parallels, while meridians join the poles.

The equator is a great circle; other latitude parallels are smaller circles. Meridians combine with their opposite meridians to form great circles. Consequently, one degree of longitude does not correspond to the same ground distance at every latitude: meridians converge towards the poles. A flat grid sketch is useful for coordinates but is not an undistorted measurement map of the whole Earth.

When comparing locations, keep angular measure and surface distance separate. Roughly 111 km per degree of latitude is a useful approximation, not an exact universal conversion for every geodetic calculation. Longitude spacing varies strongly with latitude. In a map question, identify the projection, scale, and purpose before assuming that equal-looking rectangular spaces represent equal areas or distances.

Earth turns approximately 360 degrees in twenty-four mean solar hours, giving fifteen degrees per hour or four minutes per degree. A location eastward has a later local solar time than one westward, because it reaches a given solar position earlier. Local solar time and a government-defined civil time zone are different systems.

Worked example: compare 82°30′E with 70°E. The longitude difference is 12°30′, or 12.5 degrees; multiplying by four minutes gives fifty minutes. Local solar time at 82°30′E is fifty minutes ahead. Indian Standard Time corresponds to UTC+5:30 and is associated with 82°30′E; it is not reset separately to each town’s local noon.

Date changes require considering the International Date Line and the chosen direction of travel. Moving west across it advances the calendar by a day; moving east subtracts a day in the conventional rule. Its real path bends around political and geographic arrangements, so it is not an entirely straight line lying everywhere exactly on 180 degrees. Always show the longitude subtraction, east–west sign, and calendar adjustment separately when solving a time problem.