Longitude – standard geodetic definition Longitude of a place is the angular distance between the meridian of that place and which reference meridian?

Introduction / Context:
Longitude and latitude form the fundamental coordinate system for positions on Earth. Longitude measures east–west angular distance from a universally agreed reference meridian, ensuring consistency across countries and maps.

Given Data / Assumptions:

• Geodetic convention using the Prime Meridian at Greenwich, 0° longitude.
• Longitude measured east or west from 0° to 180°.
• Time-zone meridians are administrative and do not redefine longitude.

Concept / Approach:

By definition, longitude is the angle between the plane of the meridian through the point and the plane of the Greenwich meridian. National standard meridians are used to set local times (for example, IST at 82.5° E) but do not alter the geodetic definition. The international date line approximates 180° longitude but is politically adjusted and is not the reference for defining longitude.

Step-by-Step Solution:

Verification / Alternative check:

All modern charts and GPS systems express longitude relative to Greenwich, ensuring interoperability worldwide.

Why Other Options Are Wrong:

(a) applies to civil timekeeping; (b) is a political boundary near 180°; (d) mixes an administrative meridian with the geodetic reference and is therefore incorrect.

Common Pitfalls:

Assuming local time meridians determine longitude; confusing the date line with a geodetic baseline.

Final Answer:

The Greenwich (Prime) Meridian