TOPIC 4: ELEMENTARY SURVEYING | GEOGRAPHY FORM 3
Survey is the scientific and systematic measure of distance, height (altitude) and angles between various points on the ground.
Survey is the process of observing and measuring in order to determine distance, position, boundaries and elevation of physical features on the land.
Purpose of surveying Surveying means the whole process of conducting survey. It involves the whole practices that involves in taking ground measurements of distance, height and angles between various points on the ground.
The purpose of surveying includes the following:-
(i)To determine horizontal distance between points on the earth’s surface
(ii)To determine vertical distance or height between the points on the earth’s surface
(iii)To determine the area of the piece of land or plot
(iv) To determine the direction of various features on the earth’s surface
(v) To determine the location of physical and non-physical features on the earth’s surface Stages or procedures of conducting survey/surveying methods/surveying process
(1) Reconnaissance / preliminary inspection/primary surveying
Is the process of taking general view of the land to be surveyed in order to get real picture of the work to be done. It is done by visual observation of the area. During the reconnaissance the surveyor does walking around the area to be surveyed and taking general views and noting down the dominant features area, Boundaries of the area, Corners of the boundaries of the area and Other structures such as building, big trees, ponds, lakes, small hills e.t.c
Importance of reconnaissance
(i) It helps to get the full picture of the survey to be conducted
(ii) It helps for choosing the scale for map making
(iii) It makes survey for new coordinates and old coordinate easier
(iv) It shows the existing situation on a piece of paper
(2) Actual survey /secondary survey
This steps involved observing, measuring and recording direction, angles distance and elevation by using surveying equipment or tools.
(3) Presentation this involves presentation of data or information collected or recorded, the information can be presented by writing or drawing form
BRANCHES /TYPES OF LAND SURVEYING
The following is the branches of survey.
(i) Geodating survey is the type of survey which takes into consideration on account the curvature of the earth’s surface. The geodating survey is used for a large area for example at national level. Its purpose is to lay a foundation for other types of survey and research hence it need high accuracy.
(ii) Plane surveying; is the surveying which the area measured is considered as being flat or plane. The earth’s surface is projected onto a horizontal plane. Plane survey is only used in small areas for example: – building sites like schools and dispensary, Villages and wards Plane survey does not take into consideration the curvature of the earth. But it is only gives the horizontal plane as if the earth’s surface is flat or plane.
(iii) Topographical surveying; This deal with the measuring and plotting of physical features in their horizontal and vertical positions. Nature and man-made features are measured and maps are prepared to show their relative position both horizontal and vertical.
(iv) Cadastral surveying; Is the survey that deals with defining special information for construction activities and all sorts of land development Example:- small construction site, a plane survey can be used and for a bigger site geodetic survey can be used.
(v) Engineering surveying; Is the surveying which deals with obtaining special information for construction activities and all sorts of land development.
(vi) Mine surveying Is the surveying which deals with finding minerals in the ground or rocks into the earth’s crust.
(vii) Hydrographic surveying; This surveying deals with searching or finding the amount of water present different parts or place on the earth’s surface.
METHODS/TECHNIQUES OF LAND SURVEYING
Depending on how linear and angular measurements are combined, there are four types of methods /elements/technique of land surveying.
1. Chain or tape survey
2. The prismatic compass survey
3. The plane table survey
4. The technique of levelling
Is the surveying method in which linear measurements of an area are taken
Features of chain surveying
(i) It involves taking linear measurement of angular measurements.
(ii) It is suitable for small area .e.g. schools, market etc
(iii) It is suitable in flat and open areas e.g. are with no forest or no high mountains Equipment used in chain surveying
(a) A chain; This is made up of steel divided into tallies and links it is about 20m-30m long. It is used for measuring long distance on the ground
(b)Tape measure; It is made up of plastic or steel materials having the length of 10, 20 and 30 metres. It is marked in meters, feet or centimeters. It is used for measuring short distance E.g 10m
(c) Surveyor′s band; is made of a steel strip which is rolled into a metal frame with a winding handle. It is 30m, 50m or 100m long. Is used in projects where more accuracy measurement is required.
(c) Pegs; Are made up of wood ,they normally have 40cm to 50 cm long and width of 4mm squares. They are used for marking permanent stations.
(d) Ranging rod/ranging poles; Are made of wood, their length is about 6-10 feet .they are marked red and white or black so as to be seen easily. Used to mark permanent station in the survey line.
(e) Cross staff; Is a wood rod with about 6 feet long used to determine the right angle in survey line (to make off sets). Other equipments used in chain survey include an optical square, a ruler, plumb bob, field sheet and pencil. (f) Notebooks are used during field work to record data obtained. The notebook should be of good quality and 150mm x100mm in size.
(g) A hard pencil and a rubber Hard pencils are used for drawing in the field and a rubber is used to erase mistakes or errors which are made. A pencil should be HB or HHB. Other equipment/ tools used in chain survey include arrows, optical square, Plumb bob etc.
Advantages of chain surveying
1. It is suitable for surveying flat surface on the Earth’s surface, for example a school compound
2. It can be red easily and quickly
3. It is the simplest method of surveying through the old method
4. It is suitable for surveying clear areas
5. It can be easily repaired or rectified in the field
6. It tends not to attract attention.
Disadvantages of chain survey
1. They become longer or shorter due to continuous use
2. It is not suitable for surveying large areas
3. More difficult areas cannot be chain surveyed
4. Errors may be encountered due to the use of many chains and other reasons
5. It is time consuming
6. They are heavy and take too much time to open or fold
7. It is a slow method of surveying
8. It is the oldest method of surveying
THE ERRORS THAT OCCUR IN CHAIN SURVEYING
An error is a mistake or shortcoming that happens during the survey process leading to wrong measurements. It is sometimes called discrepancies.
The following are the type of error or discrepancies in chain surveying.
Cumulative (systematic) Errors
Cumulative errors are said to be systematic errors as they are one-directional hence keep on accumulating as the survey progresses.
If not checked they have serious implications to the accuracy of the survey. Errors in this class included incorrect length of the tape, page of the tape or the tape not being in line. Since the sources of these errors are known, they can be eliminated.
They can either be positive or negative errors. Positive errors shorten the measurement (e.g where the tape length is shorter that what it should be) while negative errors elongate the measurements (e.g. where the tape is longer what is should be). Errors can be eliminated by checking the equipment
Compensating Errors (accidental) errors
Compensating errors are said to be accidental errors hence cancel out and does not pose serious problem to the accuracy of the survey.
They arise as are result of not being perfect in the use of the equipment or in the whole survey process. For example, if the pull exerted on the tape in either more than or less than what should be the case, faulty results be gotten.
The effect can either be positive or negative Gross Errors These are mistakes that can be attributed to the inexperience of the leaders. These are very serious errors which although are random in accordance my lead to faulty plans and maps if not checked.
They include discontinuing the chain length (e.g. where some arrows are cost or misplaced), misreading of the tape, reading tape upside down (e.g. taking 6 to be 9), etc. these errors can be corrected by taking the necessary precautions.
OVERCOMING OBSTACLES DURING CHAINING
Types of Obstacles
1. Visual obstacles: Is an obstacle that prevents an object but the chain remains free. An example of a visual obstacle is a forest.
2. Chain obstacles: This is the obstacle where by the chain is obstructed but visually it is free Examples are rivers and ponds
3. Neither visual nor chain obstacles for example buildings
HOW TO OVERCOME THOSE OBSTACLES
1. By rectangular method
2. By triangle method
3. By using similar triangle method
By constructing rectangles Chaining had reached A and encountered an obstacle. To get to B, mark A and B with any arrow. Set of perpendiculars AC and BD high enough to clear the obstacles. Join and measure DC which now equals AB. This allows chaining to continue from B.
By constructing similar triangles To continue chaining for B, fix point C away from the obstacle. Range a pole at D to align with Ac hence AC = CD. In line with BC range another point E in line with BC. Hence BC = CE Measure ED which equals AB hence chaining can continue from B.
Obstacles which obstruct both ranging and chaining Chaining has reached B from A where an obstacle like a building has been reached. Erect equal perpendiculars AC and BD from A and B along the chain line. Along CD, range E and F beyond the obstacle. Set off perpendiculars EG and FH from E and F equal to AC. AS G and H are in line with AB, then CE equals AG.
By constructing triangles Chaining had reached A and there is the need to overcome the obstacles created by the stream to really B. Set out a perpendicular AC and mark the midpoint E.
Set out another perpendicular CD so that D, E and B are in a straight line. The 2 triangles created are congruent CD = AB which is the required length hence chaining can now proceeds from B.
IMPORTANCE OF SURVEY
The following includes the general importance of survey
(i) It helps in determine distance between various points on the ground
(ii) It helps to determine heights on the ground
(iii) It helps to determine angles on the ground
(iv) It helps in determine areas of plots of land
(v) It helps to take ground measurements for construction of various structure E.g roads, buildings e.t.c
(vi) Leveling survey helps to determine level of sloped ground
(vii) It helps to determine for sight intermediate and back sight of various points on the ground especial sloped land.
(viii) Survey is help in taking measurements to some areas where underground structure to be constructed E.g. pipe line, underground canal etc.
Leveling: Is the procedure by which the heights of the points on the Earth’s surface are determined.
The following is the equipments used in levelling
i) Leveling staff: Is a long ruler which can be made from steel material either white and black or black and rod. “Used to fix or heights on the earth’s surface”
ii) Survey Telescope: It’s used to determine the angle of position or height on the Earth’s surface
iii) Also tape, chain and pegs are used in Leveling. Used for measuring distance. Used for making station points
iv) Note book and pencils are also used in leveling process for recording or booking all necessary field work information
v) Spirit level or buble tube this is about 50 mm to 225 mm in Length mounted on a telescope. The observer taken recording or graduated telescopic staff from own position whose height is known
The producers of leveling
1. A staff is plat at station one or base station. Then the sighting instrument is put in the direction of travel when a back sight is recorded.
2. The distance from base station to the instrument is measured.
3. The staff man moves along the direction of travel ahead of the sighting instrument (telephone). This will be station two where a fore sight is recorded.
4. The sighting instrument is moved along the direction of travel ahead of the staff man. A back sight is takes and recorded.
The procedure is repeated until all the leveling is done and recorded.
Use Fullness of Leveling
– It helps to determine the relative heights on land that can be used in contour mapping.
– Leveling can be used for determination of heights or elevation of the land surface such as hills, valleys, plans, etc.
– Housing foundation, the location of industrial sites, the route of communication and sites of building can be located and determine with the help of leveling.