Map Work - Geography Form 2 Notes

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Direction

- Course upon which something is pointing to.

Methods of Showing Direction

Traditional Methods

  1. Use of Stars
    use of stars.PNG
    • - E.g. use of groups of stars called plough to find northern direction by locating the pole star and use of Southern Cross by using the brightest star which is over South Pole to find northern direction.
  1. Use of Shadows
    use of shadows.PNG
    • E.g. morning, shadow of flag pole cast to your left you are facing north, etc.
  1. Land Marks
    • Using conspicuous features such as hills, buildings even roads to get direction.

Modern Methods

  1. Land Marks
  2. Compass Direction.
    - Use of magnetic compass which has a needle which always points north.
    - It has 16 cardinal points and 4 are basic.

Bearing

  • Expression of direction in degrees of an angle.
  • It’s measured from north in a clockwise direction.

Calculation of Bearing

calculation of bearing.PNG

  • Draw N-S line through observation point.
  • Join the two points. If it’s a feature the line should end at the centre of that feature.
  • Using a protractor measure the angle between the N-S line and the line joining the 2 points in a clockwise direction.
  • Bearing is expressed in degrees, minutes and seconds. 1◦=60’(min), 1 min=60” (sec)
  • The degrees are always expressed in 3 figures e.g. 030◦

Types of Norths

types of north.PNG

  1. True North
    • Position on the globe where all longitudes meet or the direction of N. Pole.
  1. Grid North
    • Point where Eastings meet at the N. Pole.
  1. Magnetic North
    1. Point which the magnetic needle rests when left to swing freely.

Types of Bearing

  1. Grid Bearing
    Grid bearing.PNG
    • Bearing calculated from Grid North.
      • Join the two points on the topographical map using a line.
      • Measure the angle where the Eastings intersect the line joining the two points e.g. 030◦.
  1. True Bearing
    • Bearing calculated from True North. Its calculated when the type of bearing isn’t specified.
    • E.g. from our compass diagram true bearing will be 30◦-1’=29◦59’
  1. Magnetic Bearing
    • Bearing calculated from Magnetic North.
    • Position of Magnetic North changes slightly every year.

      Steps
      • Years which have elapsed × Annual change. (No need if annual change is negligible). E.g. from our compass diagram annual change =(2009-1991)×4.8’=18×4.8’’=86.4’’=1◦26.4’
      • Add to the angle between the grid and magnetic bearing 1.e. 1◦26.4’+2◦30’=3◦56.4’
      • Add to the Grid bearing (if change is towards E) or Subtract (if change is towards W). 30◦ +3◦ 56.4’=334’


Location of Places

  • Showing of position of a place or feature on a topographical map.

Methods

Use of Place Names

  • Locating a feature by using the name of the place it’s at e.g. a river in Kisumu, Nakuru, etc or if it isn’t at a named place locate by the nearest name place e.g. a meander near Garissa town.

Use of Direction, Bearing and Distance

  • This is from a stated position e.g. Locate Nakuru from Nairobi.
  • Nakuru is 157km N.W of Nairobi.

Latitudes and Longitudes

  • The main longitudes are I.D.L and Greenwich /Prime Meridian.
  • The main lines of latitudes:
    • The equator/Great Circle (0◦) which is the longest.
    • Tropic of Cancer (23½◦N) of equator.
    • Tropic of Capricorn (23½◦) south of equator.
    • The Arctic Circle (66½◦N).
    • Antarctic Circle (66 ½ ◦ S).
  • They are marked at the margins. Latitude is stated first (N or S) and longitude later (E or W) e.g. X◦N Y◦E
    • Identify a place.
    • Identify the nearest numbered latitude and longitude.
    • Estimate to the nearest 1◦.

Grid Reference

  • Grid lines: network of lines on topographical maps.
  • Numbered in small and large numbers and the large ones are used.
  • Eastings: N-S grid lines called so because they are numbered eastwards.
  • Northings: W-E grid lines called so because they are numbered northwards.
  • Grid reference is given in 4 figures or six figures. In 4 figure the nearest grid line is stated while the 6 figure is estimated in fractions by dividing the space between grid line into 10 equal parts.
  • Easting is stated first followed by northing.
  • In the example below the 4 figure grid references are:
    • A-6856
    • B-6856
    • C-6857
  • 6 figure grid references are:
    • A-675555
    • B-680560
    • C-682568
      Grid reference.PNG


Methods of Representing Relief on Topographical Maps

  • Relief is the nature of landscape e.g. plain, plateau, valleys, hills, etc.

Spot Heights

- Points on map whose positions and heights have been determined by surveyors. They are shown by a dot and a figure e.g. (.1827).

  • Advantage-show actual heights
  • Disadvantage-can’t be used to identify landforms.

Trigonometrical Stations/Points

Trigonometrical stations.PNG

  • Carefully chosen points carefully chosen and their altitude determined which ---Are used as a basis for surveying an area.
  • They are marked on the ground by concrete pillar or slab.
  • They are indicated on topographical maps by:

Isohypes/Contours and Form Lines

  • A contour is a line on a map joining all points of the same height above sea level. They are browner in colour and have heights written on them.
  • Form lines are lines drawn on a map joining places of approximately the same height above sea level. They are less brown than contours and not all have values written on them.
  • Both contours and form lines are referred to as contours.
    contours.PNG
  • Contour/Vertical interval is the difference in height between any two successive contours.

    Advantages of contours:
    • They show actual heights.
    • Can be used to identify land forms.

Pictorials

  • Showing relief by drawing landforms at approximate positions where they are found e.g. mountains, hills, valleys, etc.

    Disadvantages:
    • They obscure details behind them.
    • Don’t give height above sea level.
    • Limited variety of landforms can be accommodated.

Hachures
hachures.PNG

  • Short lines drawn to represent direction of slope.
    • On steep land they are thick and close together.
    • On gentle slopes they are thin and wide apart.
  • Their disadvantage is that they can’t be drawn on flat land.

Hill Shading

  • Showing relief by shading to show shadows where by steepest slopes which are list lit have darker shade while hill tops, surfaces of plateaus and plains and valley bottoms are well lit have lighter shade.

Layer Tinting

  • Colouring or shading land within a certain range of altitude or using a single colour with varying tones where the colour gets darker with increasing altitude.

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