Definition
A precision optical instrument mounted on a tripod, used to measure horizontal and vertical angles between fixed points on the ground. It consists of a small telescope that can rotate horizontally on a graduated circle and tilt vertically through a graduated arc, allowing the operator to sight distant objects and read the exact angles to them.
Plain English
A small telescope on a tripod that lets a surveyor measure exact angles between things on the ground. By sighting two points and reading the angles, the surveyor can work out distances and positions accurately.
Context Anchor
Pilots may encounter this term in airport construction, runway layout, obstruction surveys, or older references to airport and landing-area measurement.
Derivation
From the Latin transire, meaning 'to cross over' or 'to pass through.' The instrument is called a transit because the telescope can be flipped, or 'transited,' through the vertical to sight in the opposite direction without moving the base.
Why Pilots Care
A surveyor's transit is used to lay out the compass rose on an airport ramp where aircraft compasses are swung and calibrated. Accurate compass calibration depends on the precise magnetic headings established with this instrument.
Intuition Check
Do not read “transit” here as transportation or public transit. In this term, a transit is a precise sighting and angle-measuring instrument used by surveyors.
Example Sentence 1
The mechanic used a surveyor's transit to lay out the compass rose before swinging the aircraft's magnetic compass.
Example Sentence 2
The new taxiway layout was marked after surveyors confirmed angles with a transit before grading started.