Basic Technical Concepts - Practical Boundary Surveying - page 23

be safe in assuming that the measurements were not made by a land surveyor.
Most modern survey plans show boundary dimensions to the nearest hundredth of
a foot. For example 100.75 feet contains two decimal places. The first place right
of the decimal point indicates tenths of a foot and the second place hundredths of
a foot. A hundredth of a foot is about 1/8 of an inch (1/8″ = 0.0104′). For meas-
urements to objects where the surveyor wants to indicate less precision, dimen-
sions can be rounded to the nearest tenth of a foot (0.1) or even to the nearest
foot. The precision of a number, when noted on a plan for example, tells the reader
something about the degree of confidence that a surveyor has in the measurement.
For example, if the surveyor is measuring to the center of a roughly constructed
field stone wall which might be 3 or 4 feet wide, showing a dimension to the near-
est hundredth of a foot may be overstating the surveyor's ability to determine the
exact center of the wall. A dimension having a precision of 0.01 will indicate a
much higher level of confidence than one shown to the nearest foot. This notion
will be clarified in the section which discusses precision and accuracy.
When surveying calculations are performed, it is desirable to use additional decimal
places in order to increase precision and minimize rounding errors. The use of 3 or 4
decimal places is common for distances and an even larger number when using trigo-
nometric functions. Electronic calculators and software operate internally using a large
number of decimal places, even though only two or three places may be displayed.
All distances in deeds and in surveying are assumed to be Horizontal
Distances unless noted otherwise. The term horizontal means a level line, a line
parallel to the horizon. When measuring distances with a steel tape, particularly
when measuring up or down a hill, a level must be used to verify that each end of
the tape is held at the same elevation. A horizontal measurement is illustrated in
Fig. 4.1 . When there is a clear view of the horizon, for example along the ocean
shore, it is possible to sight along the tape and raise or lower the ends until the
tape is in line with the horizon. The tape will then be sufficiently level to make an
accurate horizontal measurement.
Fig. 4.1 Horizontal measurement