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- Level Line: A line along which all points are at the same height above mean sea level. Due to Earth's curvature, these lines are themselves curved when visualized over large distances.
Surveyors understand that at short distances (under approximately 120 meters), the curvature’s effect is minimal, allowing the practical assumption that horizontal and level lines are effectively the same. However, over longer distances, the difference becomes significant, which is why corrections for Earth’s curvature are applied during precise measurements.
Empirical Evidence Through Theodolite Measurements
By utilizing theodolites and proper correction formulas, surveyors can measure the elevation angles between points that are miles apart. The process involves: