When it is necessary to use preliminary surveying ?

KEEN OBSERVATION

survey is a basic know how about the features of land and decided to work and construction tools and building requirement

Before the commencement of any survay work,the primary survey is important because of followings, the area to be survayed throughly by the surveyor, who then think the possible arrangement of the frame work of the survey. it involve walking over the area and note the various obstacles and weather or not the selected stations are visible. the main station should be selected so that it should be visible from any where of the area and enclose the whole area. formation of well conditioned traingle, the various object which are to be located. preparation of a net hand sketch indicating the main survay stations, sub survay stations, tie stations, base line,  arrangement for framework for traingles and approximate position of different objects.

Agree with the answer given by Mr.:Waqas

To level the area equally and to identify where cutting and filling is required. 

To check the basic amenities avaliable around the area .

Essentially to use preliminary surveying  before an actual, final or decisive one. It's the first survey, meant to make the actual one easier and more-conclusive.(Aerial photography and field visit).

determining quantities and for collecting data for the designing of engineering works such as roads, railways, etc., is known as EngineeringSurvey

Before starting a project or any kind of development, a preliminary survey is required to know about the existing condition of the land, property or the subject.

Without preliminary survey, nobody can design or plan a strong, durable and cost effective realistic plan. If anybody is doing the design, projects or planning of any thing with out preliminary survey, please don't believe them and it is better to avoid them to save our money and time.