What is Surveying ?

Surveying is the science/art of map making.( To determining the relative positions or point above the earth surface or beneath the earth surface it means direct or indirect measurement of distance,direction or elevation .) To start any development activity, the relative positions of various objects in the area with respect to horizontal and vertical axes through a reference point is required. This is achieved by surveying the area. Earlier, the conventional instruments like chain, tape and levelling instruments were used. In this electronic era, modern electronic equipments like electronic distance meters (EDM) and total stations are used, to get more accurate results easily.
In this Articles :-

Q. What is surveying ?
Q. Types of Survey ?
Q. Classification of Survey ?
Q. What is Chain survey ?
Q. What is Theodolite survey ?
Q. What is Traverse survey ?
Q. What is Triangulation survey ?
Q. What is Tacheometric survey ?
Q. What is Plane table survey  ?
Q. What is Photogrammetric survey
Q. What is Aerial survey?

Preparing topo maps of talukas, districts, states and countries and showing all important features like rivers, hills, forests, lakes, towns and cities in plan and elevation (by contour lines) also forms part of surveying. When maps of large areas are to be made corrections for earth curvature are to be made for all measurements. Such survey is called geodetic surveying also.

Surveying divided into two category :-

(1) Plane Surveying.
(2) Geodetic Surveying.

(1) Plane Surveying :-

Plane surveying is that type of surveying in which the mean surface of the earth is considered as a plane and the spheroidal shape is neglected.  All triangles formed by survey lines are considered as plane triangles.  The level line is considered as straight and all plumb lines are considered parallel.  
          In everyday life we ​​are concerned with small portions of earth's surface and the above assumptions seem to be reasonable in light of the fact that the length of an arc is 12 kilometres long lying in the earth's surface is only 1 cm greater than the subtended chord and further  that the difference between the sum of the angles in a plane triangle and the sum of those in a spherical triangle is only one second for a triangle at the earth's surface having an area of ​​195 sq.  km.  

(2) Geodetic Surveying :-

Geodetic surveying is that type of surveying in which the shape of the earth is taken. All lines lying in the surface are curved lines and the triangles are spherical triangles.  It, therefore, involves spherical trigonometry.
           All geodetic surveys include work of larger magnitude and high degree of precision.  The object of geodetic survey is to determine the precise position on the surface of the earth, of a system of widely distant points which form control stations to which surveys of less precision may be referred.

Classification of the Survey :-

Survey is classified into different groups for the sutability like; Nature of the survey, objective of the survey, instrument used in the survey .

Classification based on the nature of the Survey -

 (1) Land Surveying 
(2) Marine Surveying
(3) Astronomical Survey

(1) Land Surveying 

Land Surveying is also categories three different groups :-
Land Surveying

(i) Topographical Survey :- 

Topographical Survey horizontal and vertical location of certain points by linear and angular measurements and is made to determine the natural features of a country  such as rivers, streams, lakes, woods, hills, etc.  , and such artificial features as roads, railways, canals, towns and villages. 

(ii) Cadastral Survey :-

Cadastral survey are made incident to the fixing of property lines, the calculation of land area, or the transfer of land property from one owner to another.  They are also made to fix the boundaries of municipalities and of state and federal jurisdictions.  


(iii) City Surveying :- 

City Surveying are made in connection with the construction of streets, water supply systems, sewers and other works.  

(2) Marine Survey

 Marine or hydrographic survey deals with bodies of water for purpose of navigation, water supply, harbor works or for the determination of mean sea level.  The work consists in measurement of discharge of streams, making topographic survey of shores and banks, taking and locating soundings to determine the depth of water and observing the fluctuations of the ocean tide. 

(3) Astronomical Survey  

The Astronomical survey offers the surveyor means of determining the absolute location of any point or the absolute location and direction of any line on the surface of the earth.  This consists in observations to the heavenly bodies such as the sun or any fixed star.

Classification based on the objective of the Survey -

 (1) Engineering Survey - This is expanded for the determination of quantities or to afford sufficient data for the designing of engineering works such as roads and reservoirs, or those connected with sewage disposal or water supply.  
(2) Military Survey - This is used for determining points of strategic importance.  
(3) Mine Survey - This is used for the exploring mineral wealth.  
(4) Geological Survey - This is used for determining different strata in the earth's crust.  
(5) Archaeological Survey - This is used for unearthing relics of antiquity.

Classification based on the instrument used -

(1)  Chain survey 
(2)  Theodolite survey 
(3)  Traverse survey 
(4)  Triangulation survey 
(5)  Tacheometric survey 
(6)  Plane table survey  
(7)  Photogrammetric survey
(8)  Aerial survey

(1)  Chain survey :-

Chain surveying is that type of surveying in which only linear measurements are made in the field.  This type of surveying is suitable for surveys of small extent on open ground to secure data for exact description of the boundaries of a piece of land or to take simple details.  The principle of chain survey or chain triangulation, as is sometimes called, is to provide a skeleton or framework consisting of a number of connected triangles, as triangle is the only simple figure that can be plotted from the lengths of its sides measured in the field  .  To get good results in plotting, the framework should consist of triangles which are as nearly equilateral as possible.

(2)  Theodolite survey :-

Theodolite is the most precise instrument designed for the measurement of horizontal and vertical angles and has wide applicability in surveying such as laying off horizontal angles, locating points on line, prolonging survey lines, improving grades, determining difference in elevation, setting out  curves etc.  
       Theodolites may be classified Transit theodolite or Non - transit theodolite

(3)  Traverse survey :-

Traverse survey is that type of survey in which a number of connected survey lines form the framework and the directions and lengths of the survey lines are measured with the help of an angle (or direction) measuring instrument and a tape (or chain) respectively.  
        When the lines form a circuit which ends at the starting point, it is known as a closed traverse. If the circuit ends elsewhere, it is said to be an open traverse.

(4)  Triangulation survey :-

Triangulation survey is  horizontal control in Geodetic survey is established either by triangulation or by precise traverse.  In triangulation survey tracing and measurement of a triangle network for determining the point and position of an area , 
         the system consists of a number of inter - connected triangles in which the length of only one line, called the base line, and the angles of the triangles are measured very precisely.  Knowing the length of one side and the three angles, the lengths of the other two sides of each triangle can be computed.  The apexes of the triangles are known as the triangulation stations and the whole figure is called the triangulation system or triangulation fig.

(5)  Tacheometric survey :-

Tacheometric survey is a branch of angular surveying in which the horizontal and vertical distances of points are obtained by optical means as opposed to the ordinary slower process of measurements by tape or chain.  
      The method is very rapid and convenient.  Although the accuracy of Tacheometry in general compares unfavorably with that of chaining, it is best adapted in obstacles such as steep and broken ground, deep ravines, stretches of water or swamp and so on, which make chaining difficult or impossible.  The accuracy attained is such that under favourable conditions the error will not exceed 1/1000, and if the purpose of a survey does not require greater accuracy, the method is unexcelled. The primary object of tacheometry is the preparation of contoured maps or plans requiring both the horizontal as well as vertical control.  Also on surveys of higher accuracy, it provides a check on distances measured with the tape.

(6)  Plane table survey :-

Plane table survey is a graphical method of survey in which the field observations and plotting proceed simultaneously.  It is means of making a manuscript map in the field while the ground can be seen by the topographer and without intermediate steps of recording and transcribing field notes.  
         It can be used to tie topography by.existing control and to carry its own control systems by triangulation or traverse and by lines of levels.

(7)  Photogrammetric survey :-

Photogrammetric survey is the science and art of obtaining accurate measurements use of photographs, for various purposes such as the construction of planimetric and topographic maps, classification of soils, interpretation of geology, acquisition of military intelligence and the preparation of composite pictures of  the ground.  The photographs are taken either from the air or from station on the ground. 

(8)  Aerial survey :-

Aerial survey is that survey wherein the photographs are taken by a camera mounted in an aircraft flying over the area.  Mapping from aerial photographs is the best mapping procedure yet developed for large projects, and are invaluable for military intelligence.
        The major users of aerial mapping methods are the civilian and military mapping agencies of the Government.