Geodetic datum
Also called: WGS-84, Everest spheroid · Topic: Maps and Map Scale · NCERT: Beyond NCERT
Meaning
A geodetic datum is the model of the earth's shape used to fix coordinates (latitude and longitude). The earth is not a perfect ball, so map makers pick a model that fits it. Old Indian maps used the Everest spheroid (1830). GPS and India's Open Series Maps use the global WGS-84 datum. Because the two models differ, the same point can have slightly different coordinates on old and new map sheets.
Example
A temple in Dehradun read from an old Survey of India sheet based on the Everest spheroid may show coordinates a little different from a phone GPS reading. The phone uses WGS-84. Both describe the same spot.
Don't confuse with
- Map projection: a projection turns the curved earth onto a flat sheet. A datum is the model of the earth's shape that the coordinates are based on.
Related concepts
- Survey of India
- Map series
- Great Trigonometrical Survey
- Pundits
- National Atlas and Thematic Mapping Organisation