Call Us: +234913 605 7163
Geography
Geography
REPRESENTATION OF RELIEF FORMS
REPRESENTATION OF RELIEF FORMS
Relief of an area refers to the position and character of the Highlands and lowlands. Ways of representing these relief on maps include the following:
1) Contour: A contour is a line drawn to join places of equal height level or altitude. Contour lines are drawn at regular interval.
Contour interval: contour or vertical interval is the difference between two immediate contour lines in a map. Contours are of equal intervals in a particular map.
NOTE: when the relief is low small counter intervals are used example 50m, 100m. But when great heights are involved intervals of 200m, 250 m are used. When the contours are widely spaced they indicate a gentle slope but when they are very close together they indicate steep slope and high relief.
2) Form lines: These are lines drawn on a map like contours but are based on estimations. That is, they are not as accurate as contours and are represented by broken lines.
3) Benchmark: This is a permanent Mark made an object such as walls buildings and bridges. It shows the actual heights of the objects. They are represented by BM or ⬆️BM and the height written beside. e.g ⬆️BM450,➡️BM500.
4) Contour layering: These are different shades of colours used in showing differences in height of a place and other features on maps. E.g. green is used for lowlands, yellow and brown for highlands, white for snow-capped peaks blue for water bodies like seas. Thus; the deeper the sea, the darker the blue colour.
5) Hill shading: Here, only one colour is used but the thickness or the intensity of the colour tone depends on the steepness of the Hill slope. That is, the colour increases as the height and steepness increases.
6) Hatchures: These are short lines drawn down the slope in the direction of the steepest 5gradient. As the steepness increases the number of lines drawn increases.
7) Spot heights these are spots or points on the map whose height above the sea level has been accurately measured. e.g.⏺️100,⏺️1450,etc.
8) Trigonometrical stations: These are points on the ground showing the angles of triangulation during mapping of an area. This is shown in form of a triangle and a dot inside it with the height written by the side. We have three types of trigonometrical stations, namely;
Primary trigonometrical station. e.g. ?1500
Secondary trigonometrical station. e.g ?1000
Minor trigonometrical station. e.g ⏺️800
THE GRID REFERENCE SYSTEM
THE GRID REFERENCE SYSTEM
The grid is a system of numbered squares, formed by vertical and horizontal lines and usually shown on map surfaces.it can also be defined as a network of horizontal and vertical lines which forms squares of uniform sizes on maps They are made up of vertical and horizontal lines running north to south and east to west. Vertical gridlines are numbered eastward and are called eastings as a result of their values increasing eastward.Horizontal grid lines are known as northngs because they increase in value nortward.The eastings and northings produces a four-figure or six figure grid reference.
IMPORTANCE OF GRID REFERENCE
a)grid reference enables us to determine the position of a place accurately.
b)it helps the map reader to reduce or enlarge the original map extract to a given size.
In giving the grid reference of any feature on the, map the eastings are always given first before they nortings.e.g. the four-figure grid reference on the diagram is 4322 while the six- figure grid system on the same diagram is 415 215.
DIRECTION AND BEARING
WEEK2
DIRECTION AND BEARING
Direction- The direction of a place/ one place or object from another is expressed by using compass points or cardinal points. We have four compass/ cardinal points; namely: North, South, East and west. However, as geographers the eight cardinal points gives a more accurate result in the description of the direction of a place. Thus; North, North- East, North- West, South, South- East, South- West, East & West. We also have the sixteen cardinal points used at advanced levels.
PROCEDURES FOR MEASURING DIRECTION
1) Locate the two places involved on the map.
2) Place your four cardinal points at the place where you are to determine the direction of the other place.
3) Use your ruler and join the two places with a straight line and check which of the eight cardinal points that falls on the line.
4) The cardinal point on that line or near it is the direction of the place.
Example: what is the direction of Enugu from Onitsha on the sketch map below?
The direction of Enugu from Onitsha is South- west.
BEARING: The position of a place in relation to another is expressed as it's bearing. Bearing is expressed in degrees using a protractor.
PROCEDURES FOR MEASURING BEARING
1) Locate the two places involved on the map.
2) Place your four cardinal points at Onitsha because you are looking for the bearing of Enugu from Onitsha.
3) Use your ruler and join Onitsha to Enugu with a straight line.
4) Place your protractor on the line and the degree which falls on that line becomes the bearing. Using the above example, the bearing of Enugu from Onitsha would be around 225 degrees or less because the direction is South- west.
TYPES OF NORTHS
There are three types of NORTHS, namely:
1) True North: This is derived from a line of longitude (meridian) in the direction of the North Pole.
2) Grid North: This is the direction shown by the North- South grid lines on the map.
3) Magnetic North: This is obtained through the use of magnetic compass. It is the direction to which the needle of a simple compass always points.
The angle between the magnetic north and the true north is MAGNETIC VARIATION/ DECLINATION.
