Surveying

Surveying is the practice—part technique, profession, art, and science—of figuring out where points are on the Earth's surface by measuring the distances and angles between them. These points are typically on the ground and are used to create maps and mark property lines, as well as to pinpoint locations for building projects, the surface positions of underground features, and other needs dictated by law, like selling land. Someone who works in this field is called a land surveyor.

Surveyors draw on knowledge from geodesy, geometry, trigonometry, regression analysis, physics, engineering, metrology, programming, and law. Their tools include total stations, robotic total stations, theodolites, GNSS receivers, retroreflectors, 3D scanners, lidar sensors, radios, inclinometers, handheld tablets, optical and digital levels, subsurface locators, drones, GIS, and surveying software.

Surveying has been part of shaping human environments since recorded history began. It is essential for planning and carrying out most construction, as well as for transportation, communications, mapping, and setting legal land boundaries. It also serves as a key research tool across many scientific fields.

The International Federation of Surveyors describes a surveyor as a professional with the academic background and technical skills to do one or more of the following: determine, measure, and represent land, three-dimensional objects, point-fields, and trajectories; gather and interpret land and geographic information; use that information to plan and manage land, sea, and structures; and conduct research to advance these practices.

Surveying goes back to the earliest large structures. In ancient Egypt, rope stretchers used simple geometry to re-establish boundaries after the Nile's annual floods. The Great Pyramid of Giza, built around 2700 BC, shows the Egyptians’ skill, with its nearly perfect squareness and north-south alignment. The groma instrument likely came from Mesopotamia in the early first millennium BC. Stonehenge, from about 2500 BC, was laid out by prehistoric surveyors using pegs and rope. In 263 AD, mathematician Liu Hui wrote about measuring distant objects in *The Sea Island Mathematical Manual*. The Romans made surveying a profession, using it to divide conquered lands for tax records around 300 AD; their surveyors were called *Gromatici*. In medieval Europe, village boundaries were maintained by "beating the bounds"—walking the perimeter with residents, including young boys, to keep the memory alive. In 1086, William the Conqueror’s Domesday Book recorded landowners, land areas, quality, and details about inhabitants, though it included no maps.

In the modern era, Abel Foullon described a plane table in 1551, though it was likely used earlier. Edmund Gunter introduced Gunter's chain in 1620 for accurate land surveys. Leonard Digges described a theodolite for horizontal angles in 1571, and Joshua Habermel created one with a compass and tripod in 1576. Johnathon Sisson added a telescope to a theodolite in 1725. The 18th century saw modern techniques emerge: Jesse Ramsden built the first precision theodolite in 1787, using his own dividing engine. William Gascoigne invented a telescope with a crosshair target in 1640, and James Watt developed an optical distance meter in 1771. Willebrord Snellius introduced systematic triangulation in 1615, surveying 72 miles from Alkmaar to Breda (off by 3.5%) using 33 triangles. He showed how to correct planar formulas for Earth’s curvature and how to calculate a point’s position inside a triangle from measured angles. His work established the idea of a primary network of control points, with subsidiary points added later. Between 1733 and 1740, Jacques Cassini and his son César completed the first triangulation of France, including a re-survey of the meridian arc, leading to the first rigorous map of France in 1745. By then, triangulation methods were well established.