Tuesday, August 23, 2022

GEOGRAPHY FORM 5 TOPOGRAPHICAL MAP INTERPRETATION-MAP ORIENTATION

GEOGRAPHY FORM 5 TOPOGRAPHICAL MAP INTERPRETATION-MAP ORIENTATION

GEOGRAPHY FORM 5 TOPOGRAPHICAL MAP INTERPRETATION-MAP ORIENTATION
Tuesday, August 23, 2022

GEOGRAPHY FORM 5 TOPOGRAPHICAL MAP INTERPRETATION-MAP ORIENTATION

UNAWEZA JIPATIA NOTES ZETU KWA KUCHANGIA KIASI KIDOGO KABISA:PIGA SIMU: 0787237719





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TOPOGRAPHICAL MAP INTERPRETATION-MAP ORIENTATION

 POSITION LOCATION ON TOPOGRAPHICAL MAPS

The position location of geographical features on topographical maps with reflection to actual areas represented can be established by employing one or more of the following methods:-

  • Place naming
  • The use of latitude and longitudes
  •  Grid reference
  •  Bearing and distance

 

(a) Place naming

By this, method names of places on the topographical maps and up on the earth’s surface can be used to give the position location of a point, feature or another place e.g. the Yanga Sports club head office is at Jangwani.

 

If place naming method is used for giving position location of any geographical feature on he topographical map and up on the respective actual area represented on the earth’s surf ace, should meets the following conditions:-

  • The name of a place to be should be unambiguous i.e. some times more than one places may share the same name.
  • The name to be located should be of of significance to a person.

NB: So long the place naming method is facing a problem of ambiguity, it can be dissolved supplementing it with another method of giving location like that of grid reference or direction. E.g. the school is at Ruvu, GR 432675.



(b) The use of latitude and longitude:

It is the most useful geographical method of giving position location on the map and up on the earth’s surface. These measurements are always needed in actual making of the accurate maps. Nearly all maps indicate these along their edge though not all show these in more detail.

Both, latitudes and longitudes are really angular distance measured accurately from the centre of the earth and are expressed in degrees and further divided into smaller measurement units of minutes and seconds.

Latitude is an angular distance measured northward and southward of the line)

Longitudes are the angular distances eastwards and westward of the prime meridian.

The latitudes and longitudes are commonly used to locate the position for the wider features on the small – scaled maps or atlas maps on which these established more detailed.


MAP ORIENTATION

Procedure of giving latitudes and longitudes.

  • Firstly establish the degrees of latitudes of a place where is located from one edge to another on the map
  •  Establish the degrees of longitudes of the place on the map from obne edge to another.
  •  Combine the degree reading of both latitudes and longitudes to give the proper position location of the place.
    MAP ORIENTATION

From above Tanzania located in Latitude and longitude position of 10 30’ sand 300 to 400 E.



(c) Grid reference:-

The use of latitudes and longitude becomes  increasingly difficult for larger scaled maps. For this and others, map makers have devised a quicker and easier method known as grid reference.

A grid is a network of the evenly spaced vertical and horizontal lines drawn on the map face. The lines drawn perpendicular to one another and cross at right anglesand form the so perfect squares.

All vertical lines are called easting, because of being numbered eastwards, while the horizontal lines are numbered northwards referred to northing.

MAP ORIENTATION

 

The establishment or reading of the grid reference, it has to start by producing the numbers of easting, and then those of northing.

Grid reference can be given in four figure numbers, if the position to be located is at the exactly intersection of the vertical and horizontal grid lines. It should be in six figure numbers, if the position to be located is not at the intersection of the vertical and horizontal grid lines. However; it is always much better for the grid reference be in six figure numbers regardless of the cases.

MAP ORIENTATION

  • Point T is located at GR 403705
  • Point S is located at GR 437692

 

Note

The grid lines belong to maps. It is thus, have no reality on the ground. They do not even relate as do latitudes and longitude.



(d)Bearing and distance:

The method is mostly used to establish the location from another position by giving the degree angle measure clockwise from north and the distance of an observation line between the two positions.

Bearing is the degree angle of an observation line connecting two points on the map with reflection to an area on the earth’s surface measured clockwise from north direction.

Distance is the length of a space in between the two position points on the map with reflection to an actual area on the earth’s surface represented.

MAP ORIENTATION

 

From the above; x is located at bearing and distance of 450 and 12.5 km respectively.

 

Example:-

Determine the location of point B from point A
Bearing determination

 

Procedure:

  • Identify the two recommended points on the map by considering the grid reference or place names given. Some times both, grid reference and place names can be provided together.
  • A straight line has to be drawn to join the two end points on the map. The line represents an observation sight between the two positions in the mapped area on the earth’s surface represented.
  • Establish the four cardinal points at the position of observer. The establishment of the cardinal points should take into consideration of the north direction indicated on the map. On some of the topographical maps, the north direction is given by means of a true north.
  •  Take the protector and measure the angle of an observation line that connects two position points clockwise from north direction.

MAP ORIENTATION

The bearing of point B from point A is of about 3050



Distance determination

Procedure

  • Take into consideration of the map scale
  •  Measure the conventional distance (CD) of the observation line that connects the two points on the map.
  •  Convert the CD into AD with respect to map scale
  •  From above the CD = 10cm

Scale; 1cm represents 0.5 km

Then;

10 x 0.5 km = 5km

Thus; point B is located at bearing and distance of about 3050 and 5km respectively from point A.

Calculate the Bearing

Backwards bearing :

It is the reverse of the bearing of an object taken in front of the observer’s position along the observation line is called forward bearing. While the bearing of an object measured clock- wise from north direction backwards to the former observer’s position along the same sight line is called backward bearing. It is thus, backwards bearing s defined as the degree angle of the object measured backwards to the former observers position.

Backward bearing of an object is obtained by measuring the degree angle of an observation line clockwise from north direction backwards to former observer’s position. This can be illustrated as follows:-

  • Mark the four cardinal point at the observed object whose backward bearing to be established.
  • Take a protector and measure the degree angle of an observation line clockwise from north direction

Example

The backwards bearing of point b from point A can be established as follows:-
MAP ORIENTATION

Thus; the backward bearing of point b from point A is of about 1250



Note

If the forward bearing of the object has been established, the backwards bearing can be determined by mathematical procedure.

BB = FB + 1800

 

BB = FB + 1800 if the FB IS LESS THAN 1800

BB = FB – 1800 if the FB IS GREATER THAN 1800

 

From the above case

The FB = 3050

3050 (FB) > 1800

THUS ; The BB = 1250

 

Significance of the backward bearing

Backwards bearing is determined purposely to check the accuracy (correctness) of the forward bearing which has been taken in front of the observer’s position to an object along the sight line. It is checked by observation the difference in degrees between the BB and FB.

Always the standard difference should be 1800 if the difference is less or greater than 1800 the reading has been subjected to an error and thus needs correction to make proper determination.

 

Correction of errors

Correction of errors is attempted with the use of the mean error but considering the varied cases.

Mean error is computed by making the following application:-

Mean error = Amount of error in degree

                                     2

 

Amount of error = The different between BB & FB – 1800

 

The correction of errors with the use of mean error is done by making the following applications:-

When BB > FB

FB + Mean error BB – Mean error

 

When BB < FB

FB – Mean error & bb + Mean error




DIRECTIONS

Direction means the course or a line along which a person or thing moves or locks or which must be taken to reach a destination.

Direction on the map can e given in four, eight or sixteen cardinal points of compass and their corresponding angular bearings.

MAP ORIENTATION

MAP ORIENTATION

MAP ORIENTATION

Note:-

One land direction measured with the use of magnetic compass. The magnetic compass has a needle which always points to the north.

MAP ORIENTATION

ALIGNMENT OF ELONGATED OBJECT.

Alignment is defined as a general direction and bearing of an elongated object on the map and up on the earth’s surface measured from the central position along the straight line. Elongated object can be of like that of a road, railway, ridge, coastline, river and others of the same nature.

Alignment is best described by stating both, direction and bearing E.g. the road aligns from 450 to 2250 (SW)




Steps involved in giving the alignment

  • Identification of two end points on the topographical map given. The end points can be identified by taking into consideration of the grid reference or place names given.
  • Drawing of the straight fine line using a ruler and pencil to join the two points.
  • At the central point of the drawn line mark the four cardinal points.
  • Take a protector and measure both degree angles in which the drawn straight line trends.

MAP ORIENTATION

The alignment the coastline is from 0680 (ENE) to 2480 (WSW)

 

EXERCISE

Qn. Calculate the forward and backward bearing of Ryamugasire island grid 930340 from buhare home economics training centre grid 868324 (NECTA 2005 – Map extract of musoma sheet 12/2)

Qn. Calculate the forward and backward of Songea town at Grid reference 829169 (NECTA 2003 – Map extract of SONGEA sheet 299/1)

Qn. The compass bearing takes from a fishing boat to Samgoro hill and pump house Gr 045647 were 1450 and 1220 respectively.

Qn. By using grid reference write the position of the fishing boat.

Qn. Find the true bearing of the Samgoro from pump house (NECTA – 2002 the map of part of KENYA – NYAKWERE)

Qn. The compasses bearing of Lugongo and Kiamera hills were 1300 and 1490 respectively. These bearings were taken from a steamer on the lake.

Qn. Give the grid reference of the position of the steamer

(ii) Measure the distance in kilometers from the position of the steamer to Kaswanga pt :

(NECTA 1994-The map extract of Rusinga island)

Qn.An amateur surveyor recorded 87º as forward bearing from Goi Hill to Sangasanga hill, and 263 as his backward bearing.

(i) Correct the discrepancy of these readings.

(ii) State the importance backwards bearing.

(NECTA-2001, the map extract of KONDOA (sheet104/4.

Qn. Give the bearing of:

(i) The Masonic Lodge from Kibwesi

(ii) Tanzania packers factory from kiutu peak .

In each case, give the backward bearing.State the rule that enable you to check the correctness of your bearing (NECTA 1992 Extract, map of Arusha)

Qn. Determine the trend alignment of part from Raska zone grid reference 137417 to grid reference 148360 (NECTA – 2008 extract map of TANGA sheet 130/1)

Qn. Locate the position of Njoro school (NECTA 1997 – Extract map of Moshi Series y. 742)

Qn. (a) Find the trend of the major road from mwanza city to Musoma.

(b) Show the alignment of the railway line (NECTA 2004 – Extract map of Mwanza sheet # 33/2)




KINDS OF NORTH INDICATED ON TOPOGRAPHICAL MAP.

On most of the topographical maps, varied north are shown and these include rthe following:-

  • Magnetic north (MN)
  • True north (TN)
  •  Grid north (GN)

Magnetic north

Magnetic north is the one given by the line of half arrow head on the map representing the direction of magnetic pole (earth’s magnetic field) from the mapped area.

Magnetic pole is position of natural attraction of global magnetism

The direction of magnetic pole is detected by a needle of magnetic compass in the mapped area by the time of map construction. The needle of the magnetic compass points towards the direction where the global natural point of magnetism is located from the area to be mapped.

 

The north line on most of the African maps is not uprightly vertical . It is slightly vertical towards west as the global natural point of magnetism is located in America.

The natural point of global magnetism is found off the coast of Boothia peninsular, the north of Canada nearly price of Wales and In South is in Victoria land Antarctica.

However; the direction of magnetic pole shown on the map by magnetic north, is irregular as the natural attraction of magnetism is in water and the rate of change per year is noted.

 

True north

True north is the one given on the map as a star head line to represent the direction of global North pole (900 latitude) from the mapped area. It is parallel with the lines of longitudes.

The north pole is where all lines of longitudes meets. True north is the most useful north to geographic and it is mostly referred in the determination in position direction on the topographical map and up on the actual area represented.

The direction represented by true north does not change over the time because, the North pole is steadly constant in position.

 

Grid north

It is the unpointed north line given on the map, which follows the system of easting gridlines. This does not represent or show anything on the earth’s surface and that is why given by the un pointed line.

MAP ORIENTATION

Magnetic variation:-

Magnetic variation is an angular distance in a place from the direction magnetic pole to the direction of north pole. i.e. the measured angular distance from true north to magnetic north on the map with reflection to the actual area represented.

Always the direction of magnetic pole as represented by magnetic north on the map changes, but does not coincide with the direction of north pole (true north) This makes a considerable angular distance in between of the two direction does not remain the same at the time due to the irregulaties of the magnetic field on the earth’s surface and thus, give to magnetic variation.

 

MAP ORIENTATION

Magnetic variation is 70 14 W




Magnetic bearing:-

It is a degree angle of an observation line of a place to another place measured clockwise from the direction of magnetic pole. This is not rigid as the direction of magnetic pole is irregular.

MAP ORIENTATION

True bearing:-

It is a degree angle of an observation line of a place to another place measured clockwise from the direction of north pole. The angle on the map is measured clockwise from north pole towards the line of the observation. This is rigid as the direction of North pole from any place is steadily constant.

D:\..\..\thlb\cr\tz\__i__images__i__\tearing_magne.png

Magnetic variation projection:-

For some wishing to determine (project) magnetic variation of a place on the earth’s surface with reference to the previous one,has to make the following fundamental steps.

(1) Data analysis as per the details (content) available.With respect to this, the following should be recognized.

  • The previous recorded magnetic variation.
  • The date when the last magnetic variation has been recorded.
  • The current date whose magnetic variation to be projected.
  • The rate of change per certain given defined period of time like, year, month etc

2. Determination of the time interval by subtracting the old date from the new date.

i.e.

Time interval = T2 – T1

 

3. Determination of the total change of magnetic variation by multiplying the rate of change with the determined time interval.

4. Get the new magnetic variation of the place by making addition or subtraction to the past magnetic variation. Addition is made if there is positive change: while, subtraction is made if there is negative change.




Exercise

Qn. Town Z had magnetic variation of 320 42 by march 1980, what was the new magnetic variation of the place by December 1990, if the rate of change is 10’ per annum positively.

Qn. Town X in west Africa had MB and TB of 450 23’12’’ and 250 34’57” respectively by January 1990. If the rate of change of the direction was 15’ per annum negatively, calculate the following by July 2005.

(i)Magnetic variation

(ii) True bearing

(iii)  Magnetic bearing

Qn. (a) Differentiate between magnetic bearing and True bearing.

(b) Town X had magnetic variation of about 340 21”by November 1982. What was the new magnetic variation of the same town by February 1993, if rate of decrease stood at 15’
annually.

Qn.  Differentiate between the magnetic north, True north and grid north (NECTA 1995)

Qn. (i) Define true bearing and magnetic bearing.

(ii) January 1945 the magnetic variation over town X.

 

Grid bearing

It is a degree angle of an observation line of a place to another place measured clockwise from the grid north.

D:\..\..\thlb\cr\tz\__i__images__i__\gn2.png

The conversation of magnetic bearing into true bearing

To convert magnetic bearing into true bearing, some one has to take into consideration of the direction of magnetic pole relatively to the direction of north pole.

  •  If the direction of magnetic ole is to west of north pole direction on the map and up on the earth’s surface, true bearing of the place is obtained by applying the following formula.

 

D:\..\..\thlb\cr\tz\__i__images__i__\ROC_nnn1.png

 

TB=MB – MV

450 – 150 26 = 290 34′

 

Hence: the TB is of about 29º 34’

While:

MB = TB + MV  & MV= MB – TB

 

  •   If the direction of magnetic pole to east of the north pole direction on the map and up on the area represented, the true bearing is obtained by applying the following application.

 

D:\..\..\thlb\cr\tz\__i__images__i__\RAC_nn.png
450 + 080 18’=53º18′

Hence,The TB is of about 53018′

While:

MB = TB – MV & MV = TB – MB




EXERCISE                                                                                                                             

Qn. 9’56 If the annual decrease rate stood at 5’Find the magnetic variation of the same town in October 1966 (NECTA 1989)

Qn. (a) Define true bearing and magnetic bearing

(b) The true bearing and magnetic bearing aver town by January 1990 were 530 42 and 58’21” respectively, What can be the projected magnetic variation over the same time by july 2010 if the rate of change wood at 15’E

Qn. (MOCK)

(a)   (i) Define true north, grid north and magnetic north

(ii) Town Y had MB and TB of about 27036’ and 540 of 23” respectively by September 1982. Determine the MV. MB and TB of the same town as it was February 1993 if the rate of change stood 18’w.



GEOGRAPHY FORM 5 TOPOGRAPHICAL MAP INTERPRETATION-MAP ORIENTATION
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