The fundamental principles upon which the surveying is being carried out are: 1. Working from whole to part. 2. After deciding the position of any point, its reference must be kept from at least two permanent objects or stations whose position have already been well defined. The purpose of working from whole to part is- ● To localise the errors and ● To control the accumulation of errors. This is being achieved by establishing a hierarchy of networks of control points. The less precise networks are established within the higher precise network and thus restrict the errors