Tuesday, August 23, 2022

GEOGRAPHY FORM 5 TOPOGRAPHICAL MAP INTERPRETATION-UNDERSTANDING FEATURES ON MAPS

GEOGRAPHY FORM 5 TOPOGRAPHICAL MAP INTERPRETATION-UNDERSTANDING FEATURES ON MAPS

GEOGRAPHY FORM 5 TOPOGRAPHICAL MAP INTERPRETATION-UNDERSTANDING
FEATURES ON MAPS
Tuesday, August 23, 2022

GEOGRAPHY FORM 5 TOPOGRAPHICAL MAP INTERPRETATION-UNDERSTANDING FEATURES ON MAPS

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




ALSO READ;

  1. O’ Level Study Notes All Subjects
  2. A’ Level Study Notes All Subjects
  3. Pats Papers

TOPOGRAPHICAL MAP INTERPRETATION-UNDERSTANDING FEATURES ON MAPS

RELIEF REPRESENTATION ON MAPS

Relief refers to the physical appearance of an area by contrasting landforms. Or Variation in shapes and forms of an area over the earth’s surface.

The land forms which make the physical appearance of an area called relief features. These being landforms have defined shape and heights above the sea level.

The cartographers use to show the relief features on the maps by employning certain methods which reflect their shape and heights in response to the physical appearance of the area.

The main methods employed for this purpose include the following:-

 

1. Contouring method.

The method involves the drawing of contours (isohypes) on the map face. Contour is an imaginary line drawn on the map face connecting all points of exactly equal height above the mean sea level. The first contour map was introduced in 1791.

 

Contours as used for relief representation on large scaled maps (topographical maps) reflect shape, size and height of landforms of areas represented.

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Properties of contours as used for relief representation.

 

(a) Contours on the maps are numbered either in Meter or feet. The numbers represent the attitude values of relief features in the region mapped.
There are two numbering the contours

• The contour numbers are written on the higher Side of the contour line.
• The contour numbers are placed in the contour lines

(b) Contours are drawn in a specific interval  on the map.

(c)Contours of different elevations do not cross each Other.

(d)When Contours lie closely to one another indicate steep slope, and if observed to lie far apart indicate a gentle slope. Based to this, contours of different heights may join to form a single contour line where contours are not observed over wider part, implies the landscape is widely flat.

(e)Usually contour lines tend to join around where there is the presence of a rounded landform like; a hill, plateau, escarpment and others.

(f)Contours form V shape pointing up or down stream to indicate the presence of a river valley or spur respectively.




 Merits of contours
• Contours are the most popular and widely used method for showing relief on topographical maps.

• Contours on a topographical map can be association with other methods of showing accurate heights of the relief features of an area represented. Provide the basis for hypsometric map construction.

• Contours on a topographical map can be associated with other methods of showing relief like; spot heights, trigonometrical point and benchmarks.

• Contours on a topographical map do not hide other details.

• Contours aid in making of some ground measurements from the topographical map.e.g/gradient determination

• Provide the basis for cross section drawing from the map. Setbacks of Contours

• Some times, contours fail to show certain highest heights due to the limitation of the vertical interval used. Such heights can be shown by means of spot or trigonometric point.
• Some of the landforms are not capable for being represented by means of contours e.g. coral reefs, levees and other of the same refletion .

• Contour are  not suitable for showing relief on a small scaled map.

• It needs high skill to make interpretation on the relief features by reading the contours.

• It needs high skill to produce contours on map spot heights and form lines should be initially established ahead to contours.

• It becomes difficult to determine the exact altitudes of such parts which are not crossed by the contours.
The altitude of such parts given in estimation basis.

Setbacks of contours
Some times contours fail to show certain highest heights due to the limitation of the vertical interval used.such heights can be shown by means of sport height or trigonometric point.

 

2. Form lines

A surveyor has some times to draw contours by eyes by estimating where the contours would run between two sport heights or by sketching them in approximately (interpolating). The lines drawn in this way are called forms line. Hence forms lines are defined as the dotted and unnumbered lines drawn on the map face joining points of approximately the same heights.
Form lines are not always plotted at fixed interval and these provide the basis for establishment of contours or layer units on the map.

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    D:\..\..\thlb\cr\tz\__i__images__i__\reyna12_t1.jpg                                                        

  3. Layer tinting.
  (Layer colouring)

It is one among the most useful methods for showing relief on maps. It is by indicating distinctive colours on the map face, to contrast zones (Bands) of altitudes. The method is mostly used for Relief representation on small scale maps (atlas maps).i.e. on maps that represent very wider parts of the earth’s surface.




A map that involves the system of colours to indicate relief is called hypsometric map. The method was firstly introduced in 1878.

 

Any layer –tinted map should carry a key to interpret the different colour for varied bands of altitude. The common colours used for this purpose include the following:-

  •  Blue; represents water body. Light blue means Shallow water and dark blue means deep
  •  Green, indicates low land of either coastal plain or river valley. Pure green colourrepresents much low land with altitude from 0-200m; while; light green represent lowland of high altitude from 200-500m).
  • Yellow, indicates high land. Whitish yellow represents high lands of low altitude from 500-1000m); while pure yellow is for higher land with height from 1,000-2000m).
  •  Brown; indicates highest mountain or area with permanent ice.(2000-4000m).
  • Red or pink, indicates very high elevation with height above 4000m

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Merits of the layer tinting method.

  • It makes a map look impressive and attractive to the users.
  • It is useful method for showing relief on a small scale map.i.e on maps which represent wider  areas.
  • It is associated with the method of trigometric point. The trigonometric points provide specific exact highest altitude of particular part.
  • They give quick information to map user so long the colours easily seen on the map.

Demerits of layer tinting method.

  • It shows general altitude i.e. does not give the exact height of specific or particular point.
  • It is more expensive to produce the layer colored map
  • The method does not reflect the shape of relief features of an area on the map.
  • Always colours carry certain people’s mind. It is therefore, someone may have wrong interpretation. e.g the presence of green colour on the map may makes some one to reflect the presence of thick ever green forest.
  • If colours have already been used for layer tinting on the map ,can be used for other purposes on the same map.
  • It is not a complete method by itself. It relies on the presence of contours or form lines to provide the basis for colouring.

 

  4. Hachuring

The method involves the use of hachure.
Huchure is a series of small lines drawn on a map face showing the direction and steepness of slope. The lines are drawn to follow the slope of the ground or direction of the slope on which water would run. It is old method of showing relief on maps and it was devised by L.C Muller in 1788. It was later improved by Austrian topographer Johann George Lehman in 1799.

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Merits of hachuring

  • Hachure easily seen on the map and thus give quick information about the features represented.
  • Provide pictorial view of the relief features on a map.i.e they can successively communicate quit specific shapes of terrain.
  • Show clearly the direction of slopes on the map. i.e. They provide a general sense of steepness.




Demerits of hachuring.

  • Hide other details seen on the map and thus give quick information about the features represented.
  • Hachure on the map is non numeric.i.e.are not associated with height numbers of relief features represented. Thus, the map users are not in position to detect the relief heights by studying hachure.
  • Greet skill is needed to produce hachure on a map.
  • The hachure may not be maintained on constant scale.
  • The method is dying out. It is not much used for relief representation on the modern    constructed maps.

 

 5. Hill shading.
It is a method of showing relief in which some parts of the map are shaded to indicate the presence of hill, as they would appear if a light were shining on them. Usually, the slopes which face light are shaded lightly while those facing away are in shadow.

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Merits of hill shading

  • It gives pictorial view to the map user about the hills of an area shown on the map .it thus becomes easier to understand.
  • Make a map looks impressive and attractive to the users

Demerits of Hill shading.

  • Does not give heights of hill shown on the map.
  • The shades indicated on the map might hide other details.
  • It becomes difficult to determine the gradient of the hills represented so long, the hill shades not given with height numbers.
  • May not easily maintain on constant scale of the map.

 

6. The use of physiographic diagrams.

 

The method involves the drawing of diagrams on a map face reflecting the physical slope of the relief features like hills and mountains as they have been observed in the area. This conventional representation of land forms on the map, gives an impression of viewing the landforms in three dimensions.

The physiographic diagrams are also known as pictorials.

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Merits of the physiographic diagrams

  • The physiographic diagrams if appear on the map, become impressive and attractive to the map users.
  • The diagrams provide more pictorial view of the relief features representated as they more reflect the shape of the land forms represented. It is thus, becomes so much easier to understand.
  •  They are easily seen on the map and thus easy to read and provide quick information to the map users.




Demerits of Physiographic diagram

  • Hide other details.i.e may not make other details for the represented area to appear on the map.
  • Physiographic diagrams are non numeric as do not provide the heights of landforms represented thus, they do not make the map users to understand the altitudes of the represented relief features.
  • Only limited landforms can be shown. i.e. not all landforms can be shown by this particular method.
  • Not good method for the accurate maps as the physiographic diagrams cannot be maintained on the constant scale of the map.
  • The method is no longer used for relief representation on the modern constructed maps.


7. Trigonometric point.

It is a very small triangle conventional sign with a dot at its centre and value number beside to it. This is non imaginary method for relief representation on the map as trigonometric points established up on the presence of height ground station. (Trigonometric station) on the ground. It is thus, trigonometric point is indicated on the map provided the represented area has trigonometric station.

The number given with the trigonometric point represents the highest altitude of the land scape

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Merits of the trigonometric point.

  • It is easy to indicate trigonometric point on the map by the cartographer
  •  It is non imaginary method for relief representation on the map.
  •  Enables the map users to recognize the highest relief height very easily.
  •  It shows the accurate relief height as it was measured more accurately in are above the sea level or from a recognized reference point of bench mark.
  • Sometimes. it assists the contouring method in showing certain relief heights due to the limitation of the contours interval used.

Demerits of the trigonometric point.

  • Not easily seen on the topographical map. It is as the topographical map shown the general geographical details of an area represented.
  • Trigonometric point on a map does not give the shape of the  relief feature represented.
  •  They are selective for showing only the highest heights of the relief features represented.

8. Spot height
It is a conventional dot (point) together with the height number on a map face. It serves imaginary method for showing relief heights as have been measured above the mean sea level. The number shows the height of a relief feature shown on the map

Merits of the Spot height.

  •  It is easy to indicate spot height on the map by the cartographer.
  •  Enables the map users to recognize the relief height very easily.
  •  It shows the accurate relief height as it was measured more accurately in the area above the sea level or from recognized reference point of a bench mark.
  •  Sometimes; it assists the contouring method in showing certain heights due to the limitation of the contours interval.
  • It shows the heights of hill summits as well as points along the interested structures




Demerits of spot height.

  • Not easily seen on the topographical map. It is so as the topographical map shows the general geographical details of an area represented.
  •  Spot height on a map does not give the shape of the relief feature represented.
  • It is imaginary method for showing relief on a map.

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9. Bench mark
It is a surveyor mark unit indicated on a wall, pillar, or building used as reference point in measuring altitudes.

Or

a point of reference used by a surveyor in measuring altitudes.

Bench marks indicated on maps following the presence of such marks in the are mapped.

Bench marks on maps appear by the conventional letter of BM together with height numbers measured on the ground.

Categories of Bench marks.

Bench marks indicated on the map and up on the landscape represented are extremely varied. Some have been established to provide permanent reference in measuring altitudes, while others provide short terms reference to measure altitudes by doing surveying. With respect to this, bench marks are categorized into two and include the following:-

Temporary bench mark
These established so closely to the site of surveyor to have continuous reference in surveying process. They use to appear by conventional letters of TBM. However; these on topographical maps do not commonly appear.

Ordinance bench marks.
      These are the fixed bench marks indicated on the map with reflection to the actual area represented. They provide permanent reference in measuring altitudes of other interested point or areas.

Merits of the bench mark.

   It is easy to indicate it on the map by the cartographer.

   It is non imaginary method for relief representation on the map.

   It shows the accurate relief height as it was measured more accurate on the landscape above the sea level.



Demerits of the bench mark.

   Not easily seen on the topographical map. It is as the topographical map shows the general geographical details of an area represented.

   Bench mark on a map does not give the shape of the relief feature represented.

Asses yourself!

         Are you able to describe the different methods of showing relief on maps?

         Do you understand the application of the different methods as used for relief representation?

         Are able to narrate the merits and demerits of the methods as used to show relief on the map?

EXERCISE
Q.   (i) why contours are considered to be the most useful ways of showing  relief? (NETA 2007).
(ii) Explain the demerits of using hartures to represent relief on the map (NECTA – 2007).

Q. Outline and describe the different methods employed by the map maker to show the exact height of relief features on the map (NECTA 1997).

Q.    (i) Describe the methods used to portray the relief features on the map.
(ii) Which other methods may have been used to depict the relief features on the map? (NECTA 2003, The map extract of Songea sheet 299/1).

Q. Describe any two demerits of hill shading as a method of representing relief on the map. (NECTA 2002).
                                                                          

CARTOGRAPHIC SYMBOL AND SIGN

Topographical maps are drawn for geographical studies do not show the natural and artificial features as they appear in real life on the earth’s surface. Some of the selected conventional signs and symbols used to serve this purpose, and these are collectively referred to cartographic symbols and signs.

Hence the cartographic symbols and signs are defined as the conventional signs and symbols inserted on a face of a topographical map representing the natural and artificial features of an area mapped.
They act as language of map to provide geographical details of areas represented.
The cartographic symbols and signs are used to represent the natural and cultural features on the topographical maps, should have the following qualities.

• Should be correctly and clearly shown on the map.
• They should be easy to read.
• Easy to understand and interpret

Note.

Symbols are those used in maps which look like the natural and artificial features represented, while the signs are those which do not look like the natural and artificial features represented.



CLASSIFICATION OF THE CARTOGRAPHIC  SYMBOLS AND SIGNS

Cartographic symbols and signs are extremely varied and thus, classified into different types. They are classified according to their form of appearance on the map, and nature of data shown on the map.
According to the form of appearance, cartographic symbols and signs classified into the following types:-

Point cartographic sign:-
These are the cartographic signs in form of dots inserted on the map face. They are employed to show positional data on the mp. i.e. show a specific point on the map and up on the earth’s surface there a certain object or place occurs.

Line cartographic symbols:-
These are the conventional symbols, which take linear distinctive form of appearance on the map. They are employed to represent the elongated objects on the map with reflection to an area represented. Examples of the elongated objects represented by the line cartographic symbols are of; power transmission lines, roads, railway and administrative boundaries.

Areal cartographic sign:-
It is the conventional representation established on the map by which a continuous distinctive shade or tone employed to show a feature that covers wider part. Such features include; swaps, plantation, lakes and others.

Pictorial (descriptive) cartographic symbols:-

The conventional symbols given on the map to portray the shape of the features represented. e.g. the symbols for church, mosque, bridge and others of the same reflection.

Geometric cartographic signs:-
The conventional signs in form of geometric figures of like square, triangle, circle and other e.g. the trigonometrically point.

Letter or number cartographic signs:-
The conventional representing on a map in which one or more letter or numbers given. E.g. such for school, ch-for church, pwd – for public work department and others.
According to the nature of the features represented, cartographic symbols categorized as follow:-

Relief cartographic symbols:-

These are the symbols inserted on the map, representing the relief of an area. They include; contours, hachure, spot heights, trigonometric point and others.

(b) Transportation cartographic symbols:-

The conventional signs representing transportation systems of areas represented of like; roads, railways, air fields etc.

(c) Vegetation cerographical symbols:-

The symbols for natural and planted vegetation.

 (d) Settlements cartographic symbols:-

The symbols, which represent both rural and urban settlements of an area on the map. They include round black dots for rural settlements and black rectangle blocks for urban settlements.

(e) Water bodies (hydrograph) cartographic symbols.

These given on the map to make representation of the water body systems.

 

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Asses yourself!
Are you able to define cartographic symbols and signs?

Do you understand the main qualities of cartographic symbols and sign?

Are you able to describe the different types of cartographic symbols and signs according to different elements of variation?



CROSS SECTION, INTERVISIBILITY, HORIZONTAL EQUIVALENT AND GRADIENT.

CROSS SECTION
Cross section is a transect diagram or topographical profile of an area drawn on a paper with details taken from the topographical map to show the structural appearance of the landscape in between of the two points. It is alternatively known as relief section or topographical profile.

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Cross section is of two types and include; the simple (sketch) and annotated cross sections.

Simple-cross section is the one not drawn to scale and is made to show the general appearance of the landscape between the given points in terms of relief.

Simple cross section is drawn after estimation of the general rise and fall of the landscape. The estimation is done after the study of the contours on the given map. Beside to this,
altitudes along the vertical lines not given.

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(i)     An area to be sketched.

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(ii)    Simple cross section from A – B

The annotated cross section is the one drawn to scale and in which the position of important places and features indicated more accurately. It is also known as accurate cross
section.

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The significance of a cross section.

         Provides a clear pictorial view on the structural appearance of area in between the two places. With respect to this, a person may easily determine types of slope in the area and the appearance of the area whether undulating or un  undulating.

         It is useful for indivisibility determination between two points in the area. This is made possible as a cross section shows physical appearance of an cross section shows physical appearance of area and if clearly observed, the judgment of indivisibility becomes easier.

         It shows clearly the altitudes of the different parts of the landscape in between of the two points in the area.

         Cross section aid in making of gradient determination of the sloped landscape by relating the VI to HE.



CONSTRUCTION OF THE CROSS SECTION

The construction of cross section should fundamentally follow the following significant steps.

1. Identify and mark the two end points to be sketched on the topographical map. The points can be identified by taking into consideration of the grid references or place names given.
e.g.   A and B.
2.      2. Draw the straight line with the use of a ruler on the map to join the two identified points.

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3.    3. Take a piece of paper with a straight edge, or fold it to get straight edge and place along the drawn straight line on the map. The piece of paper has to be slightly longer than the length of
the line joining the two end points.

On the piece of paper mark the following important details.

         The two end points, which have been identified on the map.

         Where every contour line cuts the line.

         The contour heights.

         The important landscape feature of both, natural and cultural features.

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4.   Find the appropriate vertical and horizontal scales. The vertical scale is determined as follows:-

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According to the traverse on given contoured map:

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Thus; VS, 1cm represents 100m.

Vertical scale shows the relationship of height between the cross section and the actual landscape represented.



Note.

The graph space for the vertical distance of cross section lies up on a decision. Graph space should conditionally produce the vertical scale that can not results into vertical exaggeration that appears more than 10 or less than 5 as related to horizontal scale.

The horizontal scale remains to be the same to that used on the map. This provides the relationship of horizontal distance to actual ground represented.

 

 5. Construct the framework for drawing the cross section. The framework should have both vertical and horizontal line distances. The horizontal line distance is determined by the length from one point to another on the map. The measurement of the vertical line has to correspond to the decided graph space.

 

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6.Take the piece of paper which has been marked with the map details for cross section, and place along the horizontal line distance of the framework. Relate the height numbers to those allocated along the vertical line distance.

7. Connect the plotted points with pencil using the free hand to develop the structural appearance of the landscape.

8. Finish the cross section by including the following:-

      Heading; To show what the cross section is for about.

     Natural and cultural features; These if clearly indicated show the clear outlay of what is represented by the cross section.

      Vertical scale; This shows the relationship of altitudes between the cross section and actual ground represented.

   Horizontal scale; This shows the relationship of horizontal distance between the cross section and landscape represented.

        Vertical exaggeration; It shows the relationship between vertical and horizontal scale of the cross section.

        Key, if necessary.

        North direction.

        The source.

 

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Horizontal scale ; 1:50,000
Vertical scale; 1:10,000
VE = 5



VERTICAL EXAGGERATION

A cross section by its nature has both, vertical and horizontal scales. The vertical scale is nearly always subjective, while the horizontal scale is steadily constant. The vertical scale by being subjective, it can be magnified. The amount of magnification of the vertical scale over horizontal scale is known as vertical exaggeration. Vertical exaggeration is thus, defined as the amount of times by which the vertical scale is larger over horizontal scale.

Or

The relationship between the vertical scale to horizontal scale of cross section.

Vertical exaggeration is very important in cross section drawing as it determines the shape of the features represented on the cross section.

The standard vertical exaggeration of the cross section drawn from most of the topographical maps with scale of 1:50,000, is that which does not exceed 10 units and not less than 5 units.
Vertical exaggeration is principally determined by applying either one of the following two principle formula:-

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Example:-

If a cross section has the horizontal scale of 1:50,000 and vertical scale of 1:10,000, whose vertical exaggeration is determined as follows:-

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According to the cross section:-

           Horizontal scale = 1:50,000

           Vertical scale = 1:10,000

Then; 50,000

10,000

Thus, the VE = 5. This implies the vertical scale is larger for 5 times to Horizontal scale.



INTERVISIBILITY

Indivisibility is the act of establishing whether the two positions in the area as observed on the map visible to one another or not.

A good way of realizing the indivisibility of two points on the map is by drawing a cross section from one point to another to view the structural appearance of landscape. On the cross section, draw a straight line called sight line to connect the two end points.

  • If the straight line passes clearly between the two points, it implies the sighting from one point to another is not obstructed and hence, the two positions are      intervisibility.
  • If the land rises high above the sight line, implies that, the sighting from one point to another is obstructed thus, the two positions are not intervisibility.

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Factors affecting indivisibility.

Interivisibility between points on the map and up on areas on the earth’s surface effected by the following factors.

  • Relief; Natural features like mountain, hill and others in between of positions, affect intervisibility.
  • Vegetation; presence of thick forest in between of positions also affects intervisibility.
  • Buildings; the presence of tall buildings in between two positions also hinder intervisibility.




HORIZONTAL EQUIVALENT (HE).

Horizontal equivalent refers to a horizontal distance of the sloped landscape in relation to its vertical height.

Horizontal equivalent can be high, low or nil depending on the degree of a slope steepness.

Gentle slope; gives higher horizontal equivalent.
Steep slope; gives low horizontal equivalent.
Vertical slope; gives low horizontal equivalent
Horizontal equivalent is worked by converting the CD into AD with respect to map scale.

 

Example:-

Scale is 1cm=½km

CD = 10 cm

10 x½km =5 km Or 5000m.

Thus; the horizontal equivalent is 5,000m or 5km.

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GRADIENT

Gradient is a degree of slope steepness; or the ratio between the vertical interval (increase) to horizontal equivalent; or the amount of rise or fall in meter or feet of the land in relation to horizontal distance.

Gradient is determined by the following principle formula:-

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Where by:

         VI=vertical interval; It is the difference in height meter or feet between the highest and lowest altitudes of the two recommended points.

         HE = Horizontal equivalent; It is the distance between the two given points as measured from the map.



Procedure for gradient determination.

         Identify the two points and name them like A and B.

         Join the points using a straight line to form line AB.

         Measure the ground distance between the two points.

         Calculate the actual distance using map scale given to get the horizontal equivalent (HE).

         Calculate the difference in height between the two points using the contours.

         Using the formula to have the gradient.

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(a) Gradient of a slope from point A to B
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According to the given case on the map;

         Highest altitude = 1,000 m

         Lowest altitude = 200 m

         CD = 8 cm

         Scale; I cm represents 0.5km.

 

Then;

1,000m – 200m

(8 x 0.5km) x 1,000m

800 = 1

4,000 5

Thus; the gradient is 1 in 5. This implies there is a rise of 1 m high in every horizontal distance of 5m from A to B Or there is a fall of 1 m low in every horizontal distance of 5 m from B to A.

Average Gradient.

Average gradient is a degree of slope steepness for the elongated feature.The elongated feature can be of like a road, river, railway and others of the same nature.



Procedure for average gradient determination.

      Identify the two points of the elongated feature.

      Measure the length of the elongated feature on the map to get the CD.

      Convert the CD into AD b using map scale to get HE.

      Calculate the difference in height of the feature using the contours.

      Using the formula to have the gradient.

 

Example:-

D:\..\..\thlb\cr\tz\__i__images__i__\contua__t1.jpg

The average gradient for the road is determined as follow:-

D:\..\..\thlb\cr\tz\__i__images__i__\Untitled24.jpg

According to the given case on the map;

   Highest altitude = 1,460m

    Lowest altitude = 1280m

    CD =12cm

    Scale; 1cm represents 0.5km.

Then;

1,460m – 1280m

(12 x 0.5km) x 1,000m

1180 = 1

6,000 5

Thus; the average gradient of the road is 1 in 5. This implies; the road experiences a fall or rise of I m low and high respectively in every horizontal distance of 5m in between of points C and D.

Asses your self!

   Are you able to define a cross section?

   Are you able to describe the kinds of cross section?

   Are you able to narrate the significance of drawing a cross section?

    Are you able to draw a cross section?

    Are able to narrate the factors affecting intervisibility?

   Are your able to suggest intervisibility by considering cross section and affecting factors?

   Are you to define horizontal equivalent and gradient?

   Are you able to calculate gradient and horizontal equivalent.

EXERCISE

Qn. Calculate the gradient between Fotobiro hill and the point at grid reference

040640 (necta 2002 – Extract map of Nyakwere).

Qn. On the map drawn on scale of 2cms to 16 kms, there are two towns, A (altitude 800 meters and B altitude 1200 meters).

(i)  calculate the gradient of the slope if the distance between the towns measures 4.2 cm the map.

(ii)  Find the vertical exaggeration of the cross section if the vertical scale is 1:80,000. (NECTA 1997).

Qn. Draw a cross section from Mahenge peak and the western peak of Wibete

hill. (NECTA 1993; Extract map of Dodoma West sheet 162 /1).

Qn. The airfield and the top of the hill at Ilboru are 6.6kms apart. Calculate the

gradient between them (NECTA 1992; map extract part of TANZANIA – ARUSHA sheet 55/3).

Qn. Construct a neat annotated cross section from grid reference 630770 to 740770 (NECTA 1980 – the map extract part of TANZANIA – MONGOYO (Series Y742 sheet 295/1 Edition 1 TSD).

Qn. How would you determine the following on a topographical map?

Stream gradient.

Vertical exaggeration.

Horizontal equivalent (NECTA – 1983).

Qn. (i) Draw a cross section from Grid 360280 to 460330 and show area with plantation agriculture and the three major rivers.

(ii) calculate the vertical exaggeration.

(NECTA 1992 map extract part of TANZANIA – ARUSHA sheet 55/3).

Qn. Draw a cross section from point A to B , and calculate the vertical

exaggeration (NECTA 1989).

Qn. Determine the average gradient of river Kwamu kwme from grid 234626 to grid 196596. (NECTA – 2001, the map extract of KONDOa (sheet 104/4).

Qn. Calculate the gradient from Gr 000315 to Gr 020320. (NECTA – 1999, the map extract of BABATI (Y.742).

Qn. Calculate the vertical exaggeration for a topographical section across a map whose horizontal scale is one to one km and the subdivision of the vertical scale being one cm representing 50 m. (NECTA 1988).



RELIEF FEATURES IDENTIFICATION ON TOPOGRAPHICAL MAPS

Topographical maps show numerous relief features of areas represented. The relief features are widely shown by means of contours. Usually contours on maps occupy patterns with respect to the shape of the landforms (relief features). The identification of landforms on the topographical map is by looking the patterns of the contours as well as their numbers. This can be aided by drawing a cross section.

Identification of the varied landforms on the topographical maps with respect to their shape is as follows

 

1.Hill.

Hill is a rounded up land not as high as mountain.

Or

As small rounded upland of low height above the surrounding area.

On the topographical map, hill is recognized by the presence of roughly circular contours close together and the last highest contour round small space on the map.

D:\..\..\thlb\cr\tz\__i__images__i__\contu1.jpg

 

2. Plateau.

A plateau is an extensive upland with steep slopes and fairly gentle slope or flat on the top surface.

On the topographical map, plateau owning to its nature is recognized up on the presence of roughly circular contours close to one another but, the last highest contour rounds a large space on the map

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

3. Ridge.

Ridge is a big, narrow and long with steep slopes. It is recognized if there is the presence circular elongated contours close to one another.

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

4. An escarpment.

It is an upland that has gentle slope on one side and steep slope on the other side. On the topographical map, escarpment is recognized if there is the presence of roughly circular contours observed be very close to one another at one part and far part at the other side.

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

5. Slope.

Slope is a slanting piece of landscape. Or the ground that progressively falls or rises from one area to another.

There are five types of slopes and include:-

         Steep slope.

         Gentle slope.

         Concave slope.

         Convex slope.

         Vertical slope.

(a) Steep slope.

Steep slope is the one that has high degree of steepness evenly from the top to the bottom. Steep slope is recognized if on a topographical map, contours lie evenly spaced much close to one another from the top to the bottom.

D:\..\..\thlb\cr\tz\__i__images__i__\cont2.jpg

(b) Gentle slope / regular slope

Gentle slope refers to a kind of slope that has low degree of steepness more evenly from the top to the bottom.



On the topographical map, gentle slope is recognized if contours indicating the presence of slating land, observed to lie far apart evenly spaced from the top to the bottom.

D:\..\..\thlb\cr\tz\__i__images__i__\tgg2.png

 

(c) Concave slope.

It is a slanting land, which is steep at the top and gentle at bottom. Or a slope that appears to have high degree of steepness at the top and low degree of steep at bottom. Concave slope is recognized if the contours indicating slanting land, observed to be closely spaced at the top part and wider apart at the bottom.

 

(d) Convex slope.

It is the slanting land which has low degree of steepness at the top and high degree of steepness at the bottom. The contours of convex slope are close to one another at the bottom and wider apart at the top.

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

(e) Vertical slope.

It is the slope that has right angle steepness of about 90°. It is recognized if contours of different elevation join and form a single contour line.

 

D:\..\..\thlb\cr\tz\__i__images__i__\gg8_t1.png

6. Saddle or Col.

A saddle or col is a low lying land in mountain range, which connects two mountain peaks or hill. The contours of a saddle or col that enclose two mountain peaks or hills, run roughly parallel and are far apart at the low lying land.

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

 

7. Pass.

Pass is a gap through a mountain allowing a through passage to different directions. Pass on the map is recognized, if contours of mountain peaks roughly converge towards a low-lying area.

D:\..\..\thlb\cr\tz\__i__images__i__\ggg111.jpg

8. Watershed.

Watershed is a line dividing the headwaters of two or more streams flowing to different directions. On the contoured map, watershed is recognized provided the highest contours run parallel to each other and streams of water appear to diverge to different directions.

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



9.rRr     River valley:-

River valley is a long narrow and deep depression through which a river

flow. On the topographical map river valley, is recognized if the contours form V shape and the river crosses each contour.
figure here

10.  Spur:-

Spur is a projection of land or broad tongue of land from the side of a hill or mountain towards the valley. Spur is recognized if the contours form a V shape pointing down low lying area.

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

11.  Gorge.

Gorge is a deep, narrow, steeply sided river valley. The contours of a gorge are close together forming a narrow V shape pointing sharply up-stream and the river crosses each contour.

 

D:\..\..\thlb\cr\tz\__i__images__i__\ggg51.jpg

 

12.  Flood plain

A flood plain is a flat low lying area lies immediately after river channel built up by deposition of alluvium. Flood plain on the map is recognized if the contours run roughly parallel to the main river and the lowest contours are spaced enough in a way that, it marks a general width of the flood plain.
D:\..\..\thlb\cr\tz\__i__images__i__\9341.jpg

 

13. Delta:-

A delta is a flat low lying area of alluvial deposits at the mouth of the river crossed by many distributaries. On the topographical map, delta is recognized if the lowest contours follow roughly the area with tributaries.

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



14.     Estuaries:-

An estuary is a single broad river mount where a river enters a lake or  sea. The contours of an estuary are widely spaced forming the wide V shape that point up stream.

D:\..\..\thlb\cr\tz\__i__images__i__\PLLLL1.png

15.  Cliffs.

A cliff is a high rock face along a coast, river or lake. On the topographical map, cliff may be indicated in two ways.

(a)       A cliff may be shaded by short lines drawn at right angles to the coast, river or lake to indicate the steepness of it.

D:\..\..\thlb\cr\tz\__i__images__i__\cliff.jpg

(b)      Cliff on the topographical map may  also be observed by the presence of contours of different elevations, join and form a single contour line parallel to the sea, lake or river.

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

16.  Levees:-

Levees are the natural embankments built up by a stream along the edges of its channel. On a topographical map, the embankments are shown by pecked lines at right angle to the course of the river.

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

17.  Coral fringed coastline.

Coral fringed coastline is formed by a coral platform which lies close to the shore. On a topographical map, the coral fringed coastline is marked clearly by shading or by using symbols to show the area with coral fringing reef in the sea.

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

Asses your self!

  Do you understand the nature of landforms commonly shown on topographical maps?

  Are you able to identify different landforms the topographical map by considering the pattern of contours.



EXERCISE:-

Qn. (i) Describe the land forms shown on the map.

(ii) Mention two factors which have influenced the direction of tributary into tributary R

(iii)    Identify the feature at Y. (NECTA – 1988).

Qn. Describe the major landforms depicted on the map. Use the specific examples from the area (NECTA 204, the map extract of Mwanza sheet 33/2).

Qn. What type of landforms are depicted on the map? (NECTA 2008).

Qn. What features are found at grid reference,

(i) 960200? (ii)01139?

(NECTA -1993, map extract part of Tanzania-Dodoma west Sheet 162/1).

Qn. Identify the features found in the following grid readings

(I) 690110 (ii) 579145 (iii) 674063 (iv) 553123

(NECTA 2012-Uyole extract map sheet 245/3).



MAP INTERPRETATION

Map interpretation is the art of examining the given topographical map to realize the reliable geographical details of an area represented. Geographical details may include; climate, economic activities, relief, mode of transport etc.

Map interpretation is done by looking the conventional symbols and signs on the map and realize what they stand for. Map interpretation has to entails two basic processes of map reading and map analysis.

         Map reading; It is an art of examining the given topographical map to recognize the features that directed on the map.

         Map analysis; It is the art of relating the features that appear on the map to other geographical facts which are required to be described, explained or suggested.

In the process of map reading; carefully read and note; the map conventional signs and symbols, key the date of compilation, title, north direction, latitude and longitudes, and other important marginal details. However the perfect skill for interpretation of the topographical maps requires constant practices and wider geographical knowledge.

With map interpretation; some one is able to describe and explain the following geographical details:-

  •          Climate.
  •          Human activities.
  •          Vegetation.
  •          Drainage.
  •          Geological nature.
  •          Relief.
  •          Geomorphologic processes.
  •          Communication.
  •          Population distribution and settlements.

  1. CLIMATE

Climate is the average (overall) weather conditions experienced in an area especially large area for a long period of time or through out. It is thus; realization and description of climate of an area from the topographic maps is by taking into consideration of the facts much related to climate which commonly shown on the map. They considerably include the following:-

(i) Latitude:-
Climate conditions vary considerably from one latitude region to another. It is thus; if the latitude region in which the mapped area is found observed, map user may realize the more likely climatic conditions of the area with regards to the wider geographical knowledge the person has.

The latitude region is recognized by taking into consideration of the degree numbers indicated along the map edge from bottom to the top or from south to north. Such degree numbers are of latitude values. Therefore; once you are given a topographical map to establish the climate of the respective area, try to observe the latitudes of the mapped are to understand in which geographical position over earth’s surface the mapped area represented is located.



For instance:-

If the mapped area understudy is located from or in between 0° – 5° north and south of the equator,  it implies that, the area is located in the equatorial belt.If other considerations remain constant, the area is suggested to experience equatorial climatic pattern with the following conditions:-

         High rainfall through out the year with two maxima peaks i.e. there is no prolonged dry season.

         High temperature throughout the year with small annual range.

If the map along its edge shows any latitudes in between of 6° – 20° North and south of the equator. It implies the area represented on the map located in tropical region. If other considerations remain constant, the area is judged to experience tropical climatic type with conditions of:

         -Moderately high rainfall which varies annually i.e. there is the presence of both wet and dry seasons in a year.

         -Temperature is high with great annual range.

However; if the altitude is below 500m; the area can be suggested to

have coastal tropical climate with long rain season; but if altitude is above 500m, the area can be established to have continental (interior) tropical climate.


Note.

It is important for the map users to be aware with the climatic conditions experienced in varied natural regions.

(ii). Altitude.

Altitude means the height of an area from the mean sea level. Altitude has a considerable impact on climate as temperature and rainfall regime is influenced by altitudes. It is therefore, the consideration of altitude of an area from the map, may help to suggest the likely climatic conditions. With respect to this, once you are given a topographical map to suggest climate, consider the altitude of the area by reading the number of contours, spot height, bench mark and trigonometric points to realize whether the area represented on the map is of lowland or high land.

 If the altitude is higher mostly above 2000m implies the area represented is of much highland and likely to experience highland climatic pattern featured by high rains of orographical type which may vary with aspect and low annual temperature as greatly lowered by higher altitude.

 If the contours and other means show low height numbers, give an impression that, the area is of lowland and likely to experience high temperature.

(iii) Water bodies (drainage).

Drainages are very good guides to climate particularly on the relative amount of rainfall. It is so as the sources of water bodies in any are on the earth’s surface is mostly by the amount of rain fall received.

   Presence of the salt lakes, seasonal streams, boreholes, seasonal swamps and widely spaced streams suggest that, the rains in the area are seasonal with long period of dry conditions.

  Presence of abundant permanent streams and permanent swamps, suggests heavy rainfall received in the area.

  Presence of the sea, suggests maritime (coastal) climate.

 Presence of lake particularly that of Victoria reflects lake equatorial type of climate.

(iv) Natural vegetation and crops

Natural vegetation and crops shown on the map have reflection to certain climatic conditions and thus; are also good guide to climate.

Natural vegetation

  Presence of thick forests on a map and up on the respective area indicates high annual rains.

  Woodland vegetation reflects moderate high annual rains.

  Scrubs, scattered trees and thickets vegetation reflect seasonal rains.



 

Crops.

Crops are raised depending on the climatic conditions that favour their growth. Hence; the consideration of crops cultivated, helps to deduce temperature and rainfall conditions of an area observed on the map.

 Presence of coffee and tea on the map and up on the area represented, suggests cool wet climate.

 Presence of cotton, sisal and cashew nuts suggests moderately high seasonal rainfall and high temperature.

 

NOTE.

Always the suggestion of climate of an area from the topographical map, students should not rely on a single guiding fact. Consideration should be centered on more than one guiding facts. It is so in a basis that, climate is influenced by a number of varied factors. It is thus; one considered factor, may not give the absolute reality about the climate of an area.

In East Africa from which most of the topographical maps for examination purpose extracted, the following types of climate experienced.

Tropical climate.

This is experienced over most of Tanzania  exception in dry region of the central Tanzania. The climate is characterized as follows.

High temperature with great annual range and in high plateau temperatures bit lower as result of high altitude.

The amount of rainfall is moderately high and occurs in one season.

Sub tropical climate:-

It is the type of climate experienced in high land areas with in the equatorial belt. It is very common in Kilimanjaro, Kenya highlands, Kigezi, Ngara and Karagwe. The sub tropical climate is characterized as follows:-

Desert and semi desert climates:-

This type of climate is experienced in areas of central Tanzania, Northern Kenya and North eastern Kenya; and north eastern Uganda. Desert and semi desert climate is characterized as follow;-

         Temperatures are high around 27°C with very high annual range.

         Annual rainfall is generally low with long dry season.

 

Coastal Tropical climate.

This type of climate experienced along the coast of East Africa and its islands. The climate is very common in Dar es Salaam, Mombasa, Tanga and others coastal areas.

The costal tropical climate is characterized as follows:-

         Long heavy rain season.

         Temperature is high with great annual range.



Lake equatorial climate.

This is experienced around lake Victoria, in Tanzania, Kenya and Uganda. The climate is characterized by the following conditions:-

         Moderately high temperatures.

         Moderately high rain rainfall.

 

Important climate description hints.

         Produce a statement in connection to what is to be described about climate.

         Give the type of climate and its conditions.

         Establish the evidences to reinforce your description (suggestion).

D:\..\..\thlb\cr\tz\__i__images__i__\9292.png

For instance:

Qn. Describe the climate of the area.

ANSWER

Climate of the area being the overall weather conditions as observed from the given extract map is described as follows:-

The area is realized to experience equatorial climate featured by high temperatures with small annual range and high rainfall through out the year.



The realization of climate is supported (reinforced) by the following evidences as observed from the map.

The area is of latitude of 2° indicated along the map edge. Also it is of low altitude. Commonly low latitude sustain high temperature being a feature of the recognized climatic pattern.
Cultivation of cocoa reflects high rains which is also a feature of equatorial climate.

 

EXERCISE

Qn. With precise pieces of evidence propose the climate of the area shown on the map. (NECTA 2004, map extract of Mwanza sheet 33/2).

Qn. Suggest the possible climate of the area. (NECTA 1993, the extract of part of Tanzania (sheet 162/1).

Qn. Giving evidence from the map, suggest the climate of the area. (NECTA 1987, the extracts series Y 742 sheet 55/3 or ARUSHA).

Qn. Using evidence from the map, suggest the possible climate of the area (NECTA 1989).

Qn. Describe and account for the climate of the area (NECTA 1985, the extract part of Tanzania provide (sheet 55/3 series Y 742).

Qn. Comment on the possible climate of the area. (NECTA 2007, Extract map of West Hai).

Qn. Given topographical map of an area what indicators can be considered in deducing the climate of the area (NECTA 1983).

Qn. Describe how the relief and vegetation can help the map reader to depict climate on topographical maps. (NECTA 1997).

2. VEGETATION

Vegetation refers to a total assemblage of plant cover in an area. Topographical maps show vegetation with reflection to actual areas represented. It is thus; topographical maps may guide map users to realize the vegetation of an area represented.

The forms of vegetation present in East African areas of which commonly shown on topographical maps include the following:-



         Forests:- The vegetation of more close trees; or The vegetation largely dominated by dense growth of tall trees with closed leaf cover or canopy. These develop in regions with high annual rains.

         Woodland:- The type of vegetation of less closely big trees. These grown in areas with moderately high annual rains.

         Thicket :- This type of vegetation is of dense shrubs (closely shrubs) and some scattered big trees. Such vegetation nature commonly found in regions with moderately high seasonal rains.

         Scrubs:- The vegetation of less closely shrubs with widely scattered trees. Such vegetation commonly found in areas of annual seasonal rains with long dry season.

         Scattered trees:- These are the vegetation of widely spaced trees. These also commonly found in areas of seasonal rainfall.

         Planted vegetation:- Theseare more particularly of the cultivated plants (crops) like sisal, tea, coffee, cashew nuts and others.

 

The appearance of the distinctive vegetation forms on the topographical map is as follows:-

 

D:\..\..\thlb\cr\tz\__i__images__i__\image43.png

Vegetation on most of the topographical maps and up on the actual areas represented extremely varied in nature and distribution because of the following factors.

Climatic conditions

         High annual rains develop forest vegetation featured by the dense growth of trees.

         Moderately high annual rains develop woodland vegetation featured by the less closely trees.

         Moderately high seasonal rains develop thicket featured by the growth of closely shrubs.

         Seasonal rainfall makes occurrence of scrubs and scattered trees.



Relief.

It is considerably the physical appearance of an area. This influences vegetation relatively to soils and drainage as follows:-

         Where the landscape is steep as on a map contours observed to lie much closely to one another, drainage is good, but soils can be shallow. This may give to poor coverage of plants.

         Where the landscape is almost level as on the map contours observed to lie much more far apart, deep soils develop, but the area subjected to poor drainage. This also may make poor plants growth e.g. areas of seasonal swamps.

         Where the landscape is gentle sloped as on the map contours observed to lie far apart, may have deep well drained soil. This may make good coverage of plants.

Soil:-

Soil has ideal influence to plants growth in the following ways:-

         Fertile soil by being deep well drained makes good growth of plants. Such soil sustained where the topography is gentle sloped; and on the map can be realized if contours lie less closely to one another.

         Poor soil by being shallow, water logged makes poor growth of plants.

 

Human activities:-

         Areas under human utilization like; scattered cultivation and settlements, plants have been removed and thus; subjected to have poor coverage of plants.

         It is unlike to areas that not subjected to human utilization, can be observed to have good coverage of plants if other factors are also favorable.

 

Important vegetation description hits.

To describe vegetation, carefully study the map key to recognize the conventional symbols representing vegetation and relate to map face. After this the following hints can be given.

         Identify the types of vegetation shown on the map like, forest, woodland, scrub e.t.c.

         Give the distribution of each identified type of vegetation.

         Describe the extent of coverage of each identified type of vegetation.



EXERCISE

Qn. Explain the factors that have influenced the distribution of vegetation of

the mapped are (NECTA, 2006. The map extract of Mpanda 153/30).

3.   DRAINAGE

Drainage is the removal of surface water from an area by the system of both natural and man made water bodies like of rivers, lakes, swamps, ditches, canals and other related systems. The common drainage systems of areas which normally observed on the topographical maps include the following:-

 

1.      Swamps:-

A swamp is a body of shallow stagnant water that normally occupies an area of flat low lying land. Swamps normally found where the ground forms a shallow depression or is extensively flat. Swamps make drainage by receiving water drained into them by the streams of water flow in wet season.

Swamps are of different types and are shown using different symbols. The swamps are explained in the key of topographical map.

 

The different types of swamps include the following:-

         Mangrove swamp:- These on the topographical maps can only be found along the parts of the sea shore. This is because mangroves only grow in salty sea water.

 

         Tree swamps:- These are the water waterlogged areas which have trees and other smaller plants growing in them.

 

         The papyrus swamps:- These are dominated by papyrus plants.

         Marshes:- These are dominated by grasses like plants.

 

         A bog:- It is water logged spongy ground with a surface layer of decayed vegetation.

D:\..\..\thlb\cr\tz\__i__images__i__\re311.png

 

2.      Sea:-

It is a large extensive body of salty water. This makes drainage by receiving water discharged into it by rivers. The sea is usually shaded in stipples (very small dots).

 

3.      Lakes:-

These are bodies of water that occupy a basin, depression or hollow on the earth’s surface. They make drainage by receiving water drained into them by rivers and form an important inland drainage system areas.



4.      Reservoirs:-

These are the human made lakes which formed when people build dams across streams or rivers.

 

5.      Ponds:-

A pot is a small area of stagnant water which is commonly found along the stream courses. Most of the ponds are shown on the map using a dark blue tint.

 

6.      Waterholes:-

A water hole is a shallow broad pit constructed by people. It is meant to trap rain water for animals to drink. It is shown on the map using the initials WH and a small circle which precedes the initials. i.e. oWH.

 

7.      Ditches:

These are the trenches constructed in water logged areas for the purpose of draining water from the land. On topographical maps are shown by straight blue lines and the word ditch commonly written along side the line.

 

8.      Rivers:-

A  river is a mass flow of water in a natural channel from the area of upland towards the area of lowland where is likely to discharge its water.

A river can be permanent or seasonal. Permanent river can be topographical maps shown by irregular blue lines, and if the river is considerably big, the line appears thickened. While; the seasonal rivers are shown by the broken blue irregular lines. It has to bear in our mind that, some places have rivers which disappear as water percolates into the ground. Rivers of this nature on the map shown by continues irregular lines which end abruptly.

 

Drainage system of rivers occupy patterns depending on how tributaries converge to the main river and the general appearance of both consequent and subsequent streams. Drainage pattern is thus; defined as a layout made by the rivers on the landscape or is the shape produced by the arrangement of tributaries and main-river in a catchment area.



The patterns of rivers is the result of certain determinant factors which include the following.

         Slope of the land.

         The nature of the underlying rocks.

         The general relief pattern of an area.

The common river patterns of areas appearing on topographical maps include the following:-

(i)           Dendritic pattern:- It a drainage pattern in a shape of a tree trunk like structure with tributaries converged to the main river at acute angle resembling the shape of a tree like a feature. It develops on landscape of uniform rock hardness and structure and on gentle slope landscapes. It is very common in areas of igneous rocks.

 

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

 

2. Trellis or rectangular drainage pattern.

It is a pattern which occupies a shape of a lattice with tributaries converging to the main river at almost right angle. It develops on a catchment’s area whose landscape has variation in rock hardness and structure. It may also occurs in areas of faulted landscape.

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

 

(ii)   Radial pattern:- It is a drainage pattern whose tributaries diverge outwards down from the summit of rounded highland to different directions forming a shape of spokes round a wheel like structure. It is common to areas of roughly circular hills of igneous rock.

D:\..\..\thlb\cr\tz\__i__images__i__\radial.gif

(iv) Centripetal pattern:- It is the one whose tributaries flow from different directions converging at a center of down warped landscape, where there is a swamp or lake. It is largely controlled by the shape of the landscape

D:\..\..\thlb\cr\tz\__i__images__i__\centric.jpg




River course (stage) identification
It has also to be noted that, a river has its course if development marked with three stages of life cycle. The stage of a river on a topographical map can be identified as follows:-

(i)     Youthful stage.

It can be easily identified by the presence of the following;

         The narrow V – shape contours like arrow heads pointing up to highest ground.

         Very close contours along the river course, which represent steep valley sides.

         Lack of meanders.

         Absence of a flood plan.

         Very few tributaries.
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(ii)      Mature stage:-

It is recognized by the following facts on the map.

         Contours have a U – pattern crossing the river at wide interval which represent more gentle gradient.

         The landscape is fairly flat with a narrow flood plan on either side of the river.

         Presence of many tributaries.

         Low degree of meanders.

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(iii)             Old stage.

It is observed by the following facts.

         The presence of a very gentle gradient of the river course.

         Contours are very far apart cross the river.

         More pronounced meanders.

         The presence of a river broad flood plain.

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Factors influencing drainage systems.

Drainage systems observed on topographical maps with reflection to

actual areas represented are the result of the following determinant factors:-

 

(a)      Climate.

Occurrence of rainfall, supply water to surface which then development to water body systems of rivers, swamps and others as follows:-

         Heavy and continues rains, make areas to have permanent rivers and permanent swamps.

         Seasonal rains make areas to have seasonal rivers and seasonal swamps.

 

(b)      The nature of underlying rocks:-

         Impermeable underlying rocks influence the occurrence of swamps. This moreover makes rivers to flow steadily regular as water is in difficult to percolate into the ground.

         Permeable rocks make rivers to flow irregularly as may end abruptly.

         Rocks of uniform hardness influence rivers to develop either dendritic, radial and parallel patterns if other factors remain constant.

 

(c)       Relief / topography.

         Sloped topography develop rivers as water make flow from the areas of upland towards the areas of low land.

         The extensive flat low lying topography influences the occurrence of swamps as bodies of shallow stagnant water occupying flat low lying areas.

         Depressed topography encourages the occurrence of lakes. Moreover, may influence the occurrence of centripetal pattern.

         The conical shaped uplands encourage the occurrence of radial drainage pattern.

Important drainage description hints.

 When describing drainage of an area from the given topographical map, the following if possible as important hints should be given.

         Given the statement in connection to what you need to describe about the drainage of the area from the map.

         Identify the main features of drainage in the area as observed from the map. These may include; swamps, rivers, lakes, etc.

         Give the location of each feature on the map with reflection to the actual area represented.

         Give the characteristics of the identified drainage features like coverage, patterns, direction, seasonality, etc.

For instance:

Qn. Describe the drainage of the area.

ANSWER

Drainage refers to the removal of the surface water from an area by the layout of water bodies.

Therefore, the drainage of the area as observed from the given topographical map is described as follows. The area is drainage systems of river, swamps, and lake.

         Rivers; these are the flow of water in definite channels. They largely drain the area particularly the northern part where the landscape is comparatively higher and most of the rivers start to flow towards the southern part where the landscape is comparatively low. The rivers observed to occupy dendritic pattern. Some of the pronounced rivers include of Malela, Kitungwe, Kitogota, Lusingo, Kuga, Mbingu and others which might be present in the area.

         Swamps; These are the bodies of stagnant water which are observed to occupy flat low lying lands and in are all seasonal. These observed in the southern part of the area where the landscape with observation to contours is almost level. Swamps in the area make drainage by receiving surface water drained into from rivers.

 

         Lakes; These also make considerable drainage in the area. These observed in south east part where the landscape depressed. The most remarkable lake is that of Mnyamani and make drainage by receiving water discharged into it by rivers.



EXERCISE

Qn. Explain how the drainage pattern of the area is related is related to relief

(NECTA, 1993 …..THE MAP EXTRACT PART OF Tanzania – Dodoma west

(sheet 162/1).

 

Qn. Comment on the drainage pattern of the area. (NECTA 1995 – the map extract of part of Tanzania – KILWA KIVINJE (sheet 256/2).

 

Qn. Explain the main factors which have influenced the drainage system of the area. (NECTA 2000, the extract Madukani series Y742).

 

Qn. Describe the drainage pattern of the area. (NECTA 1987 the map extract

part of Tanzania provided (sheet 55/3 series Y72.)

 

Qn. Comment on the drainage in the area. (NECTA, 1985 the map extract part of Tanzania provided (sheet 55 series Y742).

 

Qn. Explain the relationship between relief and drainage of West Hai. (NECTA 2007, the map of WET HI, (sheet 56/1).

 

Qn. Explain how drainage pattern of the area is related to relief (NECTA 1991, the map extract of part of TANZANIA Fig.1).

4.ROCKS NATURE

Rocks are the aggregate or mixture of materials in solid form contented with minerals. Rocks are extremely varied and popularly include; igneous, sedimentary and metamorphic rocks.

The rocks of an area in exception of the out crop rocks and coral reefs are not directly shown on topographical maps. Rock nature can be identified by taking into consideration of the geographical facts related to geology which commonly shown on maps. These include the following:-

 

(a)      Landforms:-

Land forms are good guide to rock nature identification of an area from a topographical map.

         The presence of volcanic landforms on the map.

–          Like crater, caldera, conical hills and mountains and others, reveals the igneous rocks of both intrusive and extrusive.

         The presence of coral reef reveals the organically formed sedimentary rocks.

         The presence of depression, sand dunes, and beaches reveals existence of less resistant rocks of which easily worn out into residuals to form such landforms by accumulation.

 

(b)      Drainage features:-

Drainage features in areas strongly related to the nature of geology. It is thus; consideration of the drainage features may helps to realize the existing geological nature:-

         The presence of dendritic, parallel and radial drainage patterns reveals the presence of hard rocks. Commonly such river patters develop on landscape of uniform hard rocks.

         The presence of swamps and lake reveals the existence of impermeable underlying rocks which limit the percolation of water into the ground.



(c)       Vegetation:-

Certain vegetation much related to geological nature of areas. Therefore; the consideration of vegetation may help to suggest the nature of rock of an area.

         The presence of thick forest; and crops of coffee and tea suggest the existence of igneous rocks. It is so as such plants found where the soil is fertile. In consideration, most of fertile soils are derived from volcanic igneous rocks.

         The presence of poor vegetation suggests the existence of sedimentary rocks as such rocks have low ability to retain water for plants.

Note:-

Metamorphic rocks have poor indicators (evidence). Probably, the presence of poor vegetation may reveal the existence of such rocks.

5. RELIEF

Relief refers to the physical appearance (surface form) of an area by landforms of contrasting shape and size.

The realization and description of relief of any area from a topographical map is by observing the patterns of contours and their respective heights. The arrangement (pattern) of contours reflects the surface form physical appearance), while the numbers reflect the altitudes.

In common, the relief of the area can be of either highland or low land. The area is recognized to be of high land if is of high altitude above 500m from the mean sea level. Lowland is recognized if the area has low altitude of below 500m from the mean sea level.

 

RELIEF PATTERNS OF AREAS.

The common relief patterns recognized from the topographical maps and up on the areas represented include the following.

 

(a)      Mountain landscape:-

Mountain landscape is a surface form that rises more steeply or abruptly to summits above the surrounding area over wider area. On a topographical map mountain landscape is recognized, if contours lie so much closely to one another over a considerable wider part. Moreover; the map by contours shows many hills or summits, dissection of rivers (streams), the presence of passes, saddle, water shed and escarpments.

 

(b)      Plateau landscape:-

It is an extensive highland area, generally, level or gentle sloped at summit. On a topographical map is recognized if the landscape is assessed be of high altitude and wider part is almost level or gentle sloped. Thus; the contours observed to show higher height numbers and lie far apart to reveal a general level, and might be dissected by rivers.

 

(c)       Hilly landscape:-

It is an area predominated by numerous isolated hills. On a topographical map is recognized if the contours or roughly round close to one another appear numerous and isolated.

 

(d)      Coastal plain:-

It is an extensive area of low altitude lies immediately after the sea. The lowland Coastal plain is recognized if contours on the map are widely spaced and the elevation rarely exceed above 300m. Beside to this, the mapped area is observed to lie immediately after the sea.

 

(e)       River basin:-

The lowland of a river valley is recognized if the mapped area is observed to lie parallel to the big river and the contours show low height numbers.

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Important relief description hints.

Generally, in making description about the relief of the mapped area, the following hints should be followed.

         The map has to be divided into relief regions. This is done by observing contrasting contour arrangements.

         Give the position location of each relief region as shown on the topographical map.

         Give the general description of each relief region by giving out the prominent landforms and altitudes of each region.

EXERCISE

Qn. Describe the relief of the mapped area. (NECTA 2002, the map of part of

KENYA – NYAKWERE).

 

Qn. Describe the relief of the area shown. (NECTA 1996, the map extract Y742

55/3 or ARUSHA (reproduced from the same series).

 

Qn. What type of landscape does the map depict?

(NECTA 1995, map extract of part of Tanzania – KILWA KIVINJE (sheet

256/2).

 

Qn. With specific evidences on the map, suggest the landscape patterns that

predominate in the area.

(NECTA 2003, the map extract of SONGEA sheet 299/1).



GEOGRAPHY FORM 5 TOPOGRAPHICAL MAP INTERPRETATION-UNDERSTANDING FEATURES ON MAPS
4/ 5
Oleh

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