SURVEYING
Ss 3 Geography first Term
Subject :GEOGRAPHY
CLASS : SS 3
Term : First Term
WEEK 9 & 10
SURVEYING
Surveying refers to the marking of measurements in the field from which maps are drawn.
Aims of Surveying
(i) To determine the relative positions of both natural and artificial features
(ii) To set out on the ground the position of engineering works.
Branches of Surveying :
The branches of surveying can be classified into two, based on
(i) purpose
(ii) techniques
Purpose of Surveying
The purpose of surveying includes:
(a) Geological survey
(b) Geographical survey
(c) Cadashal survey
(d) Geodictic survey
(e) Military survey
(f) Topographical survey.
Techniques for Surveying:
The techniques for surveying include;
(1) Chain surveying
(2) Traverse surveying
(3) Hydrographic surveying
(4) Plane table surveying
(5) Triangulation surveying
(6) Aerial surveying.
Surveying Instruments and Their Uses
(i) Chain: This is used for measuring distance.
(ii) Tapes: They are used for measuring distance.
(iii) Ranging Poles: are used for viewing and alignment.
(iv) Compass: Compass is used for making bearing.
(v) Pin Arrow: Used for making points and offsets.
(vi) Theodolite: for measuring height and bearings.
(vii) Levelling Staff: Used for viewing height.
(viii) Optical Square: Used for viewing angles or bearings.
(ix) Recording Book or Field Book: Used for note taking, details, booking or recording.
(X) Umbrella: Used for shading against rain and sun.
CHAIN SURVEYING : This a particular method of surveying in which angles are measured, only linear measurements are taken in the field, A triangle is the only figure apart from a perfect rectangle which can be drawn from the lengths of the sides only and the detail of a chain survey is built upon a framework of triangles.
Apparatus for Simple Chain Survey
(a) A tape for running chain lines
(b) Arrow
(c) Measuring rod for accurate offsets
(d) An optical square
(e) Ranging poles
(f) A cross staff
(g) Steel bands
(h) Watkins clinometer
(i) Field book.
Procedure for Making Chain Survey
(1) Walk over the area and note the layout.
(2) Decide on the framework to use and drive A r in the station pegs.
(3) Sketch the layout on the chain book together with date.
TRAVERSE SURVEYING:
A traverse is a series of connected straight lines whose lengths and bearing are measured. The lines are known as legs while the points act as stations.
Types of Traverse in Surveying (a) Open Traverse: This is a traverse that is a straight line which does not close at the point of origin e.g church tower. (b) Closed Traverse: This is a traverse that connects two stations whose positions are known. E.gsurveying wood.
Methods of Traverse Surveying Prismatic Compass Traverse: It is circular magnetic compass used for surveying or taking bearing. It is a prism with a slit in it and has a sight with a vertical line opposite. It is graduated in degrees (O – 360°). The plane contains the prism slit and the sight vane hair also contains the point of the compass card.
Precautions 1. All magnetic materials should be removed from the pocket of the reader. 2. The bearing should not be observed from a position close to strongly magnetic materials. 3. The compass must be held horizontally so that the edge of the card does not rub against the top of the compass. (b) Chain Traverse: These are lines set out around the area been triangulated or measured.
(c) Theodolite Traverse: This traverse method is often used where a high degree of accuracy is required from measuring height and bearing.
Evaluation: (i) What is surveying?
(ii) State five instruments used for surveying and their uses
(iii) State the procedure for making chain surveying
(iv)State five precautions of surveying
ASSIGNMENT: Explain the following concepts vividly: (i) Open traverse (ii) Closed traverse
