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Why did electronic distance measurement make trilateration practical over large areas?

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surveying Figure 1: Photogrammetric photographs from two short, overlapping flight strips arranged for supplying mapping details. Photo-control points are shown on only one photograph; shading indicates a typical terrain feature such as a lake (see text).

Electronic distance measurement (EDM) made trilateration practical over large or hilly areas by allowing surveyors to measure distances as easily and accurately as angles.1

Before the mid-20th-century invention of EDM, trilateration was largely impractical for extensive surveying because measuring all sides of a triangle with traditional tools like tapes or chains was tedious, slow, and difficult in challenging terrain. EDM technology overcame these limitations by electronically timing the passage of radiation—such as light, infrared radiation, or radio beams—to determine distance.1

This method provides several key advantages:
* Efficiency: It eliminates the need for the complex trigonometric calculations previously required to derive side lengths from angles.21
* Versatility: Different types of radiation allow for measurements under various conditions; for instance, microwaves can penetrate atmospheric haze, fog, and foliage, which are significant obstacles in large-scale surveying.1
* Accuracy: By measuring the phase shift of a modulating signal, EDM provides the high level of precision necessary for geodetic work, ensuring that large frameworks fit together without gaps or overlaps.1