World Geography — Standard Reference Lines The great circle of longitude that passes through London (Greenwich) is called the ______.

Introduction / Context:
Map reading and timekeeping depend on globally agreed reference lines. The line of 0° longitude that passes through the Royal Observatory at Greenwich, London, is the internationally recognized starting point for measuring longitudes east and west and for defining time zones (Greenwich Mean Time/UTC offsets).

Given Data / Assumptions:

• The meridian in question goes through London (Greenwich).
• We need the correct geographical term, not latitude lines.
• Answer should name both the conventional term and its numeric value.

Concept / Approach:

Lines of longitude (meridians) run north–south; lines of latitude (parallels) run east–west. The only meridian singled out as the global zero reference is the Prime Meridian at 0°. The Equator, Tropic of Cancer, and Tropic of Capricorn are latitudes, not meridians, and therefore cannot pass “through London” as a north–south reference line.

Step-by-Step Solution:

Identify that “meridian” means longitude.Recall the special meridian through Greenwich is 0° longitude.Select “Prime Meridian (0° longitude).”

Verification / Alternative check:

Check any standard atlas legend: it marks longitudes from 0° at Greenwich, confirming the name Prime Meridian.

Why Other Options Are Wrong:

Equator / Tropic of Cancer / Tropic of Capricorn: These are latitudes; they do not describe a meridian through London.

Common Pitfalls:

Mixing up latitudes and longitudes because both are shown as “lines” on globes; remember meridians converge at poles while parallels encircle the globe east–west.

Final Answer:

Prime Meridian (0° longitude)