Surveying - The Science of Navigation - page 80

tasks, surveyors need to know about geometry and law, and also about
engineering and physics.
TYPES OF SURVEYS
We have seen that the ancient Egyptians used peg and rope to measure out
land. They did this regularly to reestablish boundaries after the annual Nile
flood washed out old markers. The professional Roman building and road
surveyors (the gromatici ) and the land surveyors ( agrimensores ) used the
groma to mark out military camps, distribute lands to army veterans (land
in conquered territory was the standard reward for service), and survey
new lands so that the emperor could establish a tax register. The caliphs
similarly employed surveyors, with their alidades and astrolabes, to map
the vast new lands acquired after the rapid Islamic expansion of the first
millennium. William the Conqueror's surveyors compiled the Domesday
Book—essentially a list of assets covering the whole of England. Later, Na-
poleon instigated cadastral surveys of his newly acquired territory. Again,
the purpose was mainly to ascertain the assets of the land of which he now
found himself master, for the purposes of taxation.
In addition to surveys for such legal or financial appraisals, for the
last four centuries there have been accurate mapping surveys. We have
seen something already of the first significant one—that of the Cassinis in
eighteenth-century France. Others followed in all the countries of Western
Europe and the New World in the eighteenth and nineteenth centuries.
The tools were compass and chain, then transit and tape, 15 and latterly,
theodolite and electronic distance measurer (EDM), or total station. Map-
ping surveys may be topographic, or they may be small-scale plane surveys
(in which the local ellipsoid of the earth can be considered a flat plane) that
look at lot boundaries—for example, as a precondition for a house loan.
Some surveys are geological; others are for engineering purposes, prior
to constructing building foundations, a tunnel, or a highway. Depending
upon urgency, scale, and budget, a survey today may be conducted by one
person on foot with a total station, or by a team of helicopters with laser
scanners. In the latter case, the helicopters' positions are fixed by GPS.
15. A transit is a type of theodolite in which the telescope can turn vertically over 180\, so
that without moving the base a surveyor can see behind as well as in front. This is useful for
traversing new territory, as when laying out new roads or rail lines. The tape is the familiar
steel tape, usually 100 feet long in the English-speaking world and graduated in units of
0.01 feet.