Linear surveying is a series of three techniques for measuring the distance between two or more locations. The three methods of linear surveying are direct surveying, optical surveying and electronic surveying. According to Ray Carlson and Associates, there are also three types of linear surveying projects: topographical surveying, boundary measurement and aerial control mapping. The most complex, aerial control mapping, measures distance and elevation.
Direct surveying is the oldest and simplest method. The Civil Engineers' Forum explains that surveyors measure distances by stretching tape, chains, strings or similar objects between two points. Direct surveying does not require technical measuring equipment, but is extremely difficult when measuring long distances. This technique is also impractical in dangerous environments such as swamps and when surveying across rivers, chasms and other inhospitable locations.
According to the New Jersey Department of Transportation, electronic surveying involves measuring distances with radio or light waves. Surveyors use their choice of equipment to generate waves, reflect them and compute the distance based on the reflection. When surveying with light waves, surveyors use a geodimeter, a machine that generates laser light and measures its reflection.
Optical surveying also relies on light waves, but not on expensive electronics. Most optical surveyors use telescopes. The Civil Engineers' Forum states this method requires excellent mathematics skills because the surveyor must triangulate the distance between two points based on raw telescope data.
Surveyors working with radio waves use one of three devices. A tellurometer is useful in extreme temperatures and over rough terrain. Decca navigators were initially used for watercraft navigation during World War II, but are also useful to surveyors. The most precise radio survey instrument is the lambda positioning system, which is especially popular for measuring distances under water.