Surveying—What Is It?
THE Egyptians called them “rope-stretchers.” Who were they? They were an ancient guild responsible for restaking land allotments for tax purposes every year after the banks of the Nile River flooded. These men were the forerunners of the modern-day professionals called land surveyors.
Today surveyors can frequently be seen alongside highways and on construction projects. You may have wondered, though, ‘What exactly is surveying?’
“Surveying has two main areas of function,” says Science and Technology Illustrated. They are “(1) to measure what exists, record where it is located, and use the data to make a map or description; or the reverse, (2) to establish landmarks in order to mark boundaries or guide construction according to such a plan or description. Surveying determines, or marks out, the position of points on, beneath, or even above the Earth’s surface.”
History of Surveying
Apparently, the first piece of land delineated was the garden of Eden. The Bible further indicates that surveyors were active in Israel, defining property boundaries and ownership. Proverbs 22:28 says: “Do not move back a boundary of long ago, which your forefathers have made.” The Romans even had a god named Terminus, who presided over boundaries and whose symbol was a stone.
Roman aqueducts and roads, many of which are still in existence, testify to the amazing accomplishments of the ancient Romans in the field of surveying. With limited means, early surveyors obtained some impressive results. In about 200 B.C.E., the Greek astronomer, mathematician, and geographer Eratosthenes calculated the earth’s circumference.
In about 62 C.E., Hero, or Heron, of Alexandria, in his book Dioptra, demonstrated the application of the science of geometry, literally meaning “earth measurements,” to surveying. And between 140 and 160 C.E., Claudius Ptolemy, following a method set out by Hipparchus, listed some 8,000 places in the known world together with their latitudes and longitudes.
By the 18th century, the Cassini family, over a period of four generations, had successfully conducted the first scientific national survey of France and produced La Carte de Cassini. The book The Shape of the World explains that “France led the way in scientific cartography; Britain was next; and the Austrian and German states close behind. In the rest of Europe national surveys caught on during the first decades of the nineteenth century.” Beyond Europe, the Great Trigonometrical Survey of India was undertaken in 1817 to complete the mapping of India. It was led by George Everest, after whom the tallest mountain in the world was renamed.
Some of the conditions under which these early surveyors worked were less than ideal. The Historical Records of the Survey of India up to 1861 reveal that fever stalked the survey team, and it was said that scarcely 1 in 70 returned to England. Other surveyors were subject to attack by wild animals or lived on starvation diets. Even so, men were attracted by the outdoor work and the measure of independence surveying gave them.
One group of Indians known as the Pundits gained special note in history for their fascinating work in Nepal and Tibet. Decrees and treaties had forbidden foreigners from entering these countries, so these surveyors disguised themselves as Buddhist lamas, or priests, to gain entry. In preparation for their undercover work, each one had been trained to pace precisely 2,000 steps to the mile [1.6 km]. A hundred-bead rosary was used to count their paces and calculate distance.
Many individuals, such as former U.S. presidents Washington, Jefferson, and Lincoln, practiced surveying to some degree. Some even credit Lincoln’s political success, in part, to his survey work, which had brought him into close contact with his fellow countrymen.
The types of land surveying usually done in our neighborhoods today fall into three categories. First, there is legal, or cadastral, surveying, which has to do with establishing legal property lines. When land needs to be subdivided for the construction of homes or when the government wants to establish the location of new streets, roads, or highways, land surveyors will be involved in apportioning the land and drawing up the legal plans.
Another type of surveying is called topographic surveying. This involves measuring and locating the size, shape, and slope of a parcel of ground as well as the location of roads, fences, trees, existing buildings, utilities, and so forth. Civil engineers, architects, structural engineers, and other professionals use the accurate location of these features on and around the piece of land that is to be developed. This information enables them to draw their plans accordingly and in some instances to incorporate these features in their designs.
Once designs, approvals, plans, and so forth are ready for a construction project to begin, there is still the matter of exactly where everything should go. At this stage a passerby will often see the third category, construction surveying, being carried out. The surveyors provide all the important points, lines, and elevation markers for the construction workers, in order to assure that all the utilities, roads, and other items are located just where the plans indicate.
Land surveys done on a small scale requiring measurements of no more than 12 miles [19 km] are called plane surveys. However, those done on a large scale require a geodetic survey, taking into account the curvature of the earth’s surface. Usually it is tied in with a country’s national coordinate grid system, which is related to lines of longitude and latitude.* This sort of work is performed to an extremely high degree of accuracy.
Modern surveying has also started to make use of special satellites through arrangements called global positioning systems. With portable devices, surveyors can now quickly locate positions on the earth’s surface with great accuracy. Other types of surveying that we may not normally be aware of include photogrammetric, photographs of the terrain taken with special cameras mounted on satellites, and hydrographic, surveys to define shorelines and determine depths and the terrain of rivers, lakes, oceans, and other bodies of water.
Importance to Us
For example, the Golden Gate Bridge in California, U.S.A., first opened in 1937. It was resurveyed in 1991 to record its precise location. If an earthquake occurs and the bridge moves, the stresses on the bridge can now be calculated and remedial action can be taken to ensure structural soundness and public safety. On a smaller scale, a ski resort in Vermont employed surveyors to improve the safety on the runs and provide world-class skiing conditions.
Further, using data obtained by satellite surveying, changes in the earth’s crust will be monitored in China in the hope that the impact of earthquakes on the population there can be reduced.* Additionally, whether it be the house you own, the roads you drive on, the office you work in, or the school you attend, all probably had a surveyor involved in their construction.
In a very tangible way, surveyors touch our lives. From using ropes to using satellites, they have sought to bring sense and order to our complex world. And as long as we continue to build and learn about the world above and beneath us, surveyors will unquestionably be needed. So the next time you see surveyors working along the roadside, you will understand a little more about their exacting profession.
For further information on longitude and latitude, see the article “Those Useful Imaginary Lines,” appearing in the March 8, 1995, issue of Awake!
For further information, see the article “Volcanoes—Are You at Risk?” in the May 8, 1996, issue of Awake!
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Electronic Distance Meter—Calculates distance by producing an electronic beam or pulse signal that is reflected back to the instrument by special mirrors positioned at the point to be located.
Theodolites and Total Stations—A theodolite (at left) measures angles and has a microscope attached to it that allows a system of lenses, internal mirrors, and prisms to display internally the greatly magnified angle measurements. Some of the more accurate theodolites can display angles as small as one second of arc, which is equal to a circle being divided up into 1,296,000 uniform parts. Total stations (at right) also have the capacity to measure electronically and to record data accumulated in the field, including angles, distances, and item descriptions. Afterward, the information can be taken back to the office and transferred to a computer for calculation and drafting purposes.
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An old-fashioned level
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Egyptian “rope-stretchers” were the forerunners of modern-day surveyors
Borromeo/Art Resource, NY