Answer:
. In topographical surveys, you measure distances along straight lines. These lines either join two fixed points or run in one direction starting from one fixed point. They are plotted in the field with pegs, pillars or ranging poles.
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Expressing distances as horizontal measurements
2. You should always measure distances as horizontal distances. You may have to measure on ground which has no slope, or only a very small slope that is less than or equal to 5 percent (see Section 4.0). The distance measured on this type of ground will be equal to or very close to the horizontal distance. When the slope of the terrain is greater than 5 percent, however, you will have to find the horizontal distance. To do this, you must either correct any measurements you made along the ground (see Section 4.0) or use another method of measurement (see following sections). Unlevelled ground also requires particular methods of measurement.
Measuring distances along lines that run through obstacles
3. Usually, you will be able to reach all the points of the straight line you want to measure. But in some cases an obstacle such as a lake, a river or a cultivated field will be in the way, and you will have to take indirect measurements. This means that you will calculate horizontal distances along the original straight line (see Section 2.9
