In a geodetic survey the surface of the earth is considered:
📝 Detailed Explanation: Geodetic vs. Plane Surveying
Surveying is broadly divided into two main types based on whether the curvature of the Earth is considered: Plane Surveying and Geodetic Surveying.
Plane Surveying (Curvature Ignored)
A plane survey is a type of survey in which the mean surface of the earth is considered as a plane and the spheroidal shape is neglected. All triangles formed by survey lines are considered as plane triangles. The curvature is so slight over a small area that ignoring it does not lead to significant errors. This method is simpler and sufficient for most engineering and construction projects. 250 square kilometres is the upper limit of the survey area for the use of a plane survey.
Geodetic Surveying (Curvature Considered)
The surveys in which the curvature of the earth is taken into consideration are known as geodetic surveying. It is used for large areas (typically more than 250 km²) and long distances where a high degree of accuracy is required. In this type of survey, the true shape of the Earth (an oblate spheroid) is taken into account. All lines lying on the surface are curved lines and the triangles are spherical triangles. This is essential for projects like establishing national boundaries or large-scale engineering works.
Because accuracy over vast distances is critical, more precise instruments and methods are employed. Angular measurements are prioritized over linear ones, as angles are less affected by the Earth's curvature than straight-line distances.
💡 Key Concepts for Students
- The Core Difference: The fundamental distinction is the assumption about the Earth's shape. Geodetic = Curved, Plane = Flat.
- Scale of Work: Geodetic surveying is for large-scale, high-precision work (e.g., national mapping). Plane surveying is for small-scale, local projects (e.g., a building site).
- Accuracy: Geodetic surveying is inherently more accurate because it models the real shape of the Earth.