Civil Engineering Reference
In-Depth Information
In conveyances, area is often described as “more or less”. In the previous exam-
ple, a deed may use language such as “containing 4.36 acres more or less”. The
“more or less” language has its origins in times before calculators and computers
were available for calculating areas. The calculation of the area of an irregularly
shaped parcel is cumbersome and time consuming to perform by hand. Because
of this difficulty, it was common before computers became widely available, to
use a
Planimeter
such as the one shown in Fig.
4.4
. A planimeter is a mechanical
device that is capable of measuring area. In operation, the planimeter is placed on
top of a drawing which depicts the boundaries of the parcel for which the area is
to be determined. One of the arms contains a needle pointer or magnifying glass at
its end. The pointer is moved around the entire perimeter of the parcel, beginning
at a particular point and ending exactly at the starting point. There is a dial which
rotates and records the amount of movement. The dial is read at the beginning and
end of the tracing movement and the difference in the reading is multiplied by a
scale factor to calculate the area.
A Planimeter is a very small, desktop, device with a limited coverage area. It
is therefore necessary to reduce the plan being traced to a size small enough so
that the planimeter can trace the perimeter of the parcel. The larger the parcel of
land, the greater the reduction in size and the less accurate the area determina-
tion becomes. It is possible to use a larger plan by breaking it up into a number of
smaller pieces and adding the areas together. Nevertheless, measuring areas using
Fig. 4.4
Polar planimeter—creative commons license
