Position on the map

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Department of Geography and Environmental
Management Map Reading and Interpretation
Adama Science and Technology University

• By Galgalo Diqa Godana.
• 2013

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POSITION (LOCATION) OF PLACES

• One of the functional uses of the map is to show
  the geographic position (location) of varied
  geographical phenomena such as mountains,
  valleys, rivers, lakes, villages, towns, Cities,
  etc.
• Position in Geographic language, simply is the
  where or location of places or objects on the
  earths surface.
• This, in fact could be relative or absolute in
  nature.
• Position by Direction and Geographic Grid
  Reference
• The geographic position of object could be shown
  by the help of either of the following
  techniques.
• Place names
• Direction and distance from a given place
• Geographical grid reference and
• National grid reference.

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a) Position by Use of Place Names

• The use of place name is known to be the most
  commonly used and simplest way of finding the
  location of a given place on earth.
• e.g. when you need to find a certain village in
  Ethiopia,
• First, get a map showing the whole country.
• Then, look all over the map until you find or
  identify the accurate position of that specific
  place market with the dot.
• In the similar way, on the world map, you can
  show the position of important place names such
  as Paris, Tokyo, Cairo, Mexico city, New York,
  London, etc.
• Despite its usefulness as the simplest and most
  easily understandable method of showing the
  location of places on maps, this techniques has
  the following shortcomings

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Cont..

1. On the small scale only the major place names are
   marked with a dot while minor place names and
   those found within the major place names as well
   are ignored.
2. All places are not universally meaningful to all
   people of the world. Thus, the place names shown
   on maps become meaningful only for people who use
   map to find (locate) them.
3. Identical (same) place names create ambiguity or
   confusion of locating them.
4. Place names changes over time .

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b) Position by Geographic Grid

• Geographic grid is a method by which the position
  of any place on the earths surface can be given
  accurately with the help of grid lines of
  parallels (latitudes) and meridians (longitudes).
• If you study a globe, or a map carefully you will
  find that two sets of lines form a network on the
  surface of it.
• One set of lines run from the North pole to the
  South pole. These lines are known as Meridians.
• The other set of lines are running around the
  globe parallel to the equator. They are known as
  parallels.
• Using this grid we can now give the accurate
  position of any place on the earths surface.
• The parallels give the position north or south of
  the equator. This is the Latitude of the place.
• The meridians, give the position to the east or
  west of the zero degree meridian(Greenwich). This
  is the longitude of the place.
• Both latitude and longitudes are given in
  degrees, minutes and seconds.

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Cont

• Measurements of the Earth
• Many scholars have attempted to arrive at the
  accurate measurement of the earths surface
• For instance, Eratosthenes, has calculated the
  circumference of the earth trigonometrically as
  40,233 km which is close to the today's value.
• Equatorial diameter 13,057 kms
• Equatorial circumferences 40,076 kms
• Meridians circumference 40,008 kms
• Polar diameter 13,013 kms

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Grid lines

• Are a series of straight lines intersecting at
  right angles forming squares.
• Horizontal grid are lines that run from west to
  east
• Vertical grid lines are lines that run from south
  to north
• BASIC RULE
• Read right on the vertical lines, then up on the
  horizontal grid lines

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Grid Lines
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21
20
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3818000mN
47
48
49
50
51
52
53
54
546000mE
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Latitudes

• Latitude lines that encircle Earth run east-west
  and measure degrees north and south of the
  Equator.
• The Equator is neither north nor south it is the
  line that divides Earth into northern and
  southern hemispheres.
• The Equator, also known as 0 degrees
  latitude, is the only latitude line that is a
  great circle.
• Latitude lines are also know as parallel lines,
  as each latitude line is parallel to the other.
• Circles of latitude get smaller and smaller as
  they approach the poles because Earth has a
  spherical shape.
• However, the distance between each line of
  latitude is the same.
• Latitude lines measure distance in degrees
  northward for 90 degrees to the North Pole and 90
  degrees southward to the South Pole. This adds up
  to 180 degrees.

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Cont
The earth latitudes
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Cont

• Certain regions on the globe receive
  perpendicular rays of the Suns energy.
• These are the hottest rays of the Sun, and so it
  is no accident that the region of the tropics is
  the hottest region.
• This only occurs between the Tropic of Cancer
  (23 1/2oN) and the Tropic of Capricorn (23 ½oS).
• Two additional special lines, the Arctic and
  Antarctic Circles, also are a result of the
  insulation received from the Sun.

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Cont

• The Circles mark the point at which Earth
  receives either 24 hours of sunlight or lack of
  sunlight, depending upon the location of Earth in
  its seasonal path around the Sun.
• Even with 24 hours of sunlight, the angle at
  which Earth receives the Suns energy rays is so
  great, little heating ocurs.
• The Arctic Circle is at 66 1/2oN of the Equator
  the Antarctic is 66 1/2oS.

66 1/2oN
231/2oN
23 ½oS
66 1/2oS
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longitudes

• Longitude lines encircle Earth running
  north-south and measuring degrees east and west
  of the Prime Meridian.
• The Prime Meridian divides Earth into an eastern
  and a western hemisphere.
• The Prime Meridian was chosen as the 0 degree
  longitude.
• The Prime Meridian is centered in Greenwich.
• Longitude lines meet and cross over each other at
  the poles.
• They are not parallel to each other in fact, the
  distance between longitude lines varies as one
  moves closer to or farther from the poles.

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Cont

• Longitude lines measure distance in degrees
  eastward and westward until they meet at 180
  degrees.
• 180 degrees is neither east nor west it depends
  on the direction of travel.
• The Eastern Hemisphere is 180 degrees, and the
  Western Hemisphere is 180 degrees for a total of
  360 degrees.
• Longitude lines are used to designate time a.m.
  ante (before) meridian and p.m. post (after)
  meridian, based on the Prime Meridian.
• However, with little travel across the Pacific
  Ocean and few land masses and people, it was
  determined that the day/date would change on the
  180 degrees line as one traveled east or west of
  that line.
• It became known as the International Date Line,
  and early in history was the same as 180 degrees.
  
• Today, however, the International Date Line
  zigzags around countries and islands, so a
  country has the same date. So, the International
  Date Line is not exactly the same as 180 degrees.

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Cont
Longitudes
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Hemispheres

• By using the equator and prime meridian, we can
  divide the world into four hemispheres, north,
  south, east, and west.

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• Together latitude and longitude create Earths
  Geographic Grid.
• This is a Cartesian coordinate system, where
  every location is on a plane of two intersecting
  lines.
• North or south of the Equator is given first and
  then the east-west location.
• Standard protocol is to use symbols for the
  mathematical description, capital letters only
  (no period) for the direction, and separation of
  latitude from longitude by a comma.

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Point A is located at 10oN, 30o W.
N
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A
10
W
E
10
20
S
10
30
20
40
30
20
10
40
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National Grid Reference and Geographic Grid

• A National grid is a network of horizontal and
  vertical lines printed on the face of a map.
• The network of grid lines border squares.
• These squares may be divided into smaller and
  smaller squares.
• National or regional grid reference is one of the
  techniques currently in use to indicate the
  position of points on maps.
• This method is based on two pairs of lines, which
  run from east to west and north to south. Those
  running from west to east are called horizontals
  or Northing. Where as which run from north to
  south are known as verticals or Easting.

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Principles of national grid reference

• While using either the four digit or six
  digit grid references , for reading national grid
  reference of any point feature you need to
  consider the following points
• Easting are always given before Nothings.
• The grid number printed in small size should be
  ignored and only the bigger number prints should
  be used.
• After taking the necessary reading, combine the
  easting and northing values with out leaving any
  gap.
• A grid reference can never be used for locating
  an area it is usually stands for a point
  features.
• The map showing grid reference for various point
  features has been divided into many boxes, called
  grid squares.
• Each grid lines has a number, written at the edge
  of the map to show distances (in meters or
  kilometers) from the grid origin.

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Cont

• Grid numbers steadily increases in two directions
  from the grid origin i.e. from left to right for
  easting and bottom to top for northing.
• The number written against each grid line refer
  to the next square along.
• There are two important methods of giving
  national grid reference on maps. These are
• The four-digit grid reference and
• The six-digit grid reference.
• FOUR-DIGIT GRID SYTEM
• As its name indicates, four digit grid
  reference is made of four numbers. The first two
  indicates Easting and the second two Nothings.
• Hence, the grid lines are drawn at an interval
  of 1000kms.
• The four - digit grid reference is used for small
  scale maps.
• Hence it is too general and less accurate than
  six digit grid reference.

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How to Find a Four Digit - Grid Reference

• In order to easily locate the position of a point
  feature using the four digit grid reference use
  the steps given below.
• Locate the vertical grid line to the left of the
  point and read the large number only.
• Measure the length of the side of the square from
  the grid line to the point.
• Locate horizontal grid line below the point and
  read the large number only.
• Measure tenth from the grid line to the point.
• Combine the easting (two numbers) and northings
  (two numbers) with out any gap, and the result
  will be the four digit grid reference for a
  given point location.

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e.g. find four digit grid reference for point
F
Scale 1 250,000
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Procedures Easting (vertical) Northing (horizontal)
1.Locate the vertical grid lines to the left of point F and read the large number. 5
2. Divide the square into ten equal divisions and pick the tenth of the point. 5
3. Locate the horizontal grid line below the point F and read the larger number. 2
4. Again divide the square into ten equal divisions and pick the tenth, 5
The grid reference for point F 55 25
The 4 digit grid reference for point F 5525 The 4 digit grid reference for point F 5525 The 4 digit grid reference for point F 5525
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six digit grid reference

• Six digit grid reference contains 6 numbers.
• The first three gives Easting while the second
  three, Northings.
• The six digit grid reference is used on large
  scale maps and it provides more detailed
  information.
• How to Find a Six Digit Grid Reference
• In order to identify the six digit grid
  reference for any point location, apply the
  following necessary steps.
• Locate the vertical grid line nearest to the left
  of the point and write two large number only.
• Measure tenth from the grid line to the point.

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Cont

• Locate horizontal grid line nearest below the
  point and write the two large number only.
• Measure tenth from the grid line to the point.
• Combine the easting (three numbers) and northings
  (three numbers) with out any gap, and the result
  will be the six digit grid reference for a
  given point location.
• e.g. Find the national 6 digit grid reference for
  the points B, F and N on the map below.

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