Offsets:

The details on ground such as fences, buildings and towers, etc. are to be located with reference to main chain lines by means of lateral measurements. These lateral measurements along with reference to the chain line are referred to as offsets. The two categories of offsets are exhibited in Figure 4. These are perpendicular offset PP1 and the oblique offset PQ. Perpendicular offsets are the lateral distances taken at right angles (normal) for the chain line. Here if the inclination of offset line to chain line is anything other than 90^o and the offsets are termed oblique offsets.

The offsets have two significant characteristics, by which they are identified, measured, recorded and referred to:

(a) Chainage on chain line at that offset is measured, i.e. chainage of point P₁ on chain line in Figure 4.

(b) Distance of offset point of interest to point P₁ on chain line, i.e. distance PP₁ in Figure 4.

Figure: Offsets