The mean sea level (MSL) adopted by the Survey of India as the reference datum for all reduced levels in India is based on observations at:
Correct Answer: D. Mumbai
📚 Detailed Explanation: Mean Sea Level (MSL) Reference in India = Mumbai (Bombay)
Why D (Mumbai) is correct: The Survey of India (SoI) established the primary datum for all reduced levels (RLs) in India by taking Mean Sea Level observations at Mumbai (formerly Bombay). All benchmarks across India are referenced to this datum.
India's Levelling Datum
| Country / Survey | MSL Reference Port / Location |
|---|---|
| India (Survey of India) | Mumbai (Bombay) — tidal gauge at Apollo Bunder |
| United Kingdom | Newlyn, Cornwall (Ordnance Datum Newlyn) |
| United States | National Geodetic Vertical Datum of 1929 (multiple tide gauges) |
| Australia | Multiple tide gauges (Australian Height Datum) |
Important Exam Fact: All RLs in Indian topographic maps, engineering projects, and benchmarks are measured above the MSL datum established at Mumbai. This is a frequently tested fact in GATE, ESE, and SSC JE exams.
- India's MSL reference: Mumbai (Bombay) — Apollo Bunder tidal gauge.
- All Indian Benchmarks (GTS, secondary, tertiary) are referenced to this datum.
- GTS = Great Trigonometric Survey benchmarks; primary network across India.