Longitude system — allowable range of values from the prime meridian From the prime meridian (0°), longitudes are conventionally measured within which range?
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A0° to 180° eastward only
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B0° to 180° westward only
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C0° to 180° east or west
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D0° to 360° eastward only
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E0° to 360° westward only
Answer
Correct Answer: 0° to 180° east or west
Explanation
Introduction / Context:In geodesy and navigation, longitude specifies the east–west position of a point on Earth relative to the prime meridian through Greenwich. Standard conventions restrict the magnitude to avoid ambiguity and ensure interoperability across maps and databases.
Given Data / Assumptions:
- Prime meridian (Greenwich) is 0° longitude.
- Earth is divided into eastern and western hemispheres.
- Standard convention uses signed longitudes or E/W suffixes.
Concept / Approach:
Longitudes are measured eastward or westward from 0° up to a maximum of 180°. The anti-meridian at 180° is shared by both east and west designations (180°E ≡ 180°W). Using 0–180° E/W avoids wrap-around issues that can occur with 0–360° notation unless a strictly positive eastward system is explicitly adopted.
Step-by-Step Solution:
Identify allowable magnitude: up to and including 180°.Allow either sign/direction: east or west.Therefore select the combined choice (east or west).Verification / Alternative check:
Most global datasets (e.g., WGS84) use either ±180° or 0–360° east-positive; the classical cartographic form is 0–180° E/W.
Why Other Options Are Wrong:
- (a) and (b) omit half the globe.
- (d) and (e) employ a 0–360° system not implied here and not standard in many surveying contexts.
Common Pitfalls:
- Mishandling 180° when converting between signed and E/W notations (east positive vs. west positive conventions).
Final Answer:
0° to 180° east or west.