Geography Reference
In-Depth Information
other places, these monumental works' locational accuracy in reference to
movements of the solar system demonstrates their creators' surveying skills.
For most of known history, surveying has been a very stable discipline,
only changing as new instrument-making technology advanced and survey
accuracy increased. If a surveyor from ancient Egypt had been able to travel
through time and go to any Western country up until the 1880s, he or she
would have found the accuracy of survey measurements greatly advanced,
but the techniques and basic instruments remarkably similar. Surveyors used
a chain of fixed length as a common instrument to measure distances for
surveys in many parts of the United States until the 20th century.
During these four millennia, surveying involved numerous techniques
that can be simplified first into distance and angle measures and second into
leveling. Distance and angle measure involved the use of a plane table to
make situation drawings “in the field” and devices such as telescopes to
make accurate measures. Leveling was done with plumb bobs and water and
mercury levels to accurately measure changes in elevation between locations
and their respective heights. Surveying was often connected to navigation
and most surveyors were capable of navigation by sextant using the stars or
sun.
Basic Field Survey Techniques
The most elementary techniques for collecting positional information only
require instruments for measuring distances and angles. Usually collected by
making drawings on a plane table (something like a breadboard kept level on
a tripod), a basic field survey starts at a point with a known position. Mea-
surements taken for a survey continue through a series of distance and angle
In-Depth The Gunther Chain
One of the unsung technical heroes of American history is certainly the Gun-
ther chain. The Gunther chain greatly simplified surveying of public land,
thereby easing the development of the western United States.
Gunther's chain was a measuring instrument 66 ft (20.1 m) long, divided
into 100 links (1 rod or perch = 25 links). Each link was a short section of wire
connected to the next link by a loop. It was long used for land surveying and
became a unit of length (80 chains=1mile). These units are still used in many
surveys.
Although its inventor Edmund Gunther invented this measuring device in
the late 16th century, it wasn't until the late 17th century that it was widely
adopted. Once adopted, it was the most common unit of measurement for
U.S. surveyors until the early 20th century. Because it was hand-made, each
chain was somewhat different in length and surveyors needed to use a table of
adjustments for this distortion and for distortions arising from heat and cold.
A surveyor also needed another person, a chain man, to help carry the chain
and look after it.
 
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