The Earth and the Graticule Class 6 Geography Notes Maharashtra State Board
Graham, Katya, Michico, Natalia, Minakshi, Shahid, and Enrike have answered the above questions differently using directions and subdirections. The Taj Mahal is located at one and the same place and that is Agra.
However, when each one of the children was told the directions from their respective places, their answers were different. This means that the use of directions alone does not help us to accurately describe the location of a place. That is why, it became necessary to find a new system to state the precise location of any place on the earth.
The figure shows the lengths of the east-west and north-south diameters of the earth. This will give you some idea about the size of the earth. Oceanic waters, the uneven nature of the land, forests, innumerable islands of different sizes, and buildings make it impossible to actually draw such lines on the earth. In order to overcome this difficulty, geographers developed a miniature model of the earth in the form of a globe. This can be used to determine locations on the earth. One can actually draw horizontal and vertical lines on a globe though not on the earth. Thus, they are imaginary lines on the earth.
Angular Distance
The location of any place on the earth is determined with reference to the center of the earth. In order to do it, we consider a straight line joining the point on the surface and the center of the earth. At the center, it makes an angle with the plane of the equator. The measure of this angle is used in determining the locations. For example, in the figure, the measure of angle XMV is 30°. That is, its angular distance from the equator is 30°. Look at the figure and tell the angular distance of ‘Y’ from the equator.
The figure shows another plane. It passes through X. It is parallel to the plane of the equator. Observe and see how it meets the surface of the earth. Note that it forms a circle on the surface. Any point on this circle and the equatorial plane form an angle of 30° at the center of the earth.
Parallels of Latitude
You must have realized that the ellipse drawn by joining the 20° points is larger than the ellipse that joins the 60° points. However, the distances XK1 and XP2 are the same. This is because we are dealing with a sphere.
Note that though these lines appear to be ellipses in the diagram, on the globe they are circles. The circles thus created at some angular distance from the center of the earth are parallel to one another. Hence, they are called parallels of these latitudes. The values of parallels are angular measures expressed in degrees.
The degrees of the parallels are measured from the equator as shown in the figure. That is why, the equator is considered as 0° parallel. It is the largest parallel, and also a great circle. The angular distance of other parallels towards north and south goes on increasing away from the equator.
The equator bisects the earth into north and south parts. The one to the north is called the northern hemisphere while the one to the south is called the southern hemisphere. Towards the north and south of the equator, parallels of latitude progressively become smaller and smaller. On the globe (and also on the earth), at the north and south ends of the earth’s axis, they appear as points. These are called the North Pole and the South Pole respectively.
While mentioning the value of a parallel, it is necessary to mention whether it is in the northern or southern hemisphere. The parallels from the northern hemisphere are referred to as 5°N, 15°N, 30°N, 50°N whereas the parallels from the southern hemisphere are referred to as 5°S, 15°S, 30°S, 50°S.
A line joining all the places located to the north of the equator at an angular distance of 30° is 30° north parallel. Hence, all the places on this parallel will be at the same latitude, which is 30°N. New Orleans in North America, Cairo in Africa, and Basra and Lhasa in Asia are all located on 30°N parallel. The same concept holds good for all other parallels.
One can draw 181 parallels on the earth at the interval of 1°.
- At 0°, that is the equator.
- 90 parallels in the northern hemisphere – 1°N to 90°N.
- 90 parallels in the southern hemisphere – 1°S to 90°S.
Take an orange and peel off its skin. You will see the segments inside and thin vertical lines on them. Carefully take out one segment. Observe the segment and the gap it has left in the orange. See if the shape of the central and terminal portions of the segment is the same or different. See if the angle of the gap is the same at all points. Find how many segments there are in an orange.
An orange is spherical, with a circular cross-section. There are 360° in a circle. The earth being spherical, we consider 360° with respect to the earth as well.
In figure, ∠ABC, ∠DEF, ∠GHI have the same measure, 50°. However, the distances between A and C, D and F, and G and I, are different when measured on the earth’s surface. That is because the Earth is spherical in shape.
Meridians of Longitude
You will realize that the lines drawn from points A, B, and C make angles at M, the center of the earth on the plane of the equator. Through these points, we can draw semicircles joining both poles. Starting with point A, we can draw similar semicircles through points placed at each degree. These semicircles are known as meridians of longitude.
One of these meridians is considered to be 0°. It is known as the Prime Meridian. The angular distances of the other meridians from the Prime Meridian are measured in degrees and are called longitudes. You have done this in the activity based on the figure. The 0° and 180° meridians lie opposite on the globe, forming a circle. This circle divides the earth in the eastern and western hemispheres. All meridians are equal in size.
Meridians in the eastern hemisphere are labeled as 10°E, 25°E, 135°E, etc. while in the western hemisphere, they are labeled as 10°W, 25°W, 135°W, etc. 30°E is the semicircle that joins all places at an angular distance of 30° from the Prime Meridian. Some of them are Cairo, Harare, and Durban in Africa.
Though the earth is huge in size, we can tell the exact location of places on the earth using latitudes and longitudes. Note that the distance between two adjacent parallels is the same everywhere but the distance between two adjacent meridians is not the same everywhere. We can see this even in the segment of an orange. The distance between the meridians is the maximum on the equator and goes on reducing towards the Poles. At the Poles, it is zero.
The distance between any two adjacent parallels is 111 km on the surface of the earth. The distance between two adjacent meridians is also 111 km on the equator. To locate the places within this distance of 111 km exactly, we need to divide the unit degree into smaller units. Degrees are divided into minutes, and minutes into seconds. Conventionally, latitudes and longitudes are expressed into degrees, minutes, and seconds. Each degree is divided into 60 minutes and a minute into 60 seconds. These values are expressed using the symbols degrees (… °), minutes (…’), and seconds (…”).
In all, we can draw 360 meridians, each at a distance of 1°.
- 0° Prime Meridian
- 180° meridian
- 1° East to 179° East meridians. Thus, we have 179 meridians in the eastern hemisphere.
- 1° West to 179° West meridians. Thus 179 meridians in the western hemisphere.
The distance between any two consecutive meridians is different on different parallels. It is maximum on the equator and it is zero on both the Poles.
- Equator – 111km.
- Tropic of Cancer/Capricorn – 102 km
- Polar Circles (Arctic/Antarctic) – 44 km
- Poles (North/South) – 0 km
The Graticule
The parallels and meridians on the globe form a net that is called a graticule. This facilitates determining the location of a place. Thus we use latitude and longitude for determining the locations on the earth. This method is being used even in today’s modern age quite effectively. Geographical Information System (GIS), Global Positioning System (GPS) as also Google Maps, Wikimapia, and Bhuvan of ISRO on the internet also make use of latitudes and longitudes. This technology is also available on mobile phones and motor cars.
Indian Regional Positioning System:
India has achieved self-reliance in Global Positioning Technology. With the help of IRNSS (Indian Regional Navigation Satellite System), locating any place in the Indian subcontinent is going to be easy. For this, India is launching its own series of 7 satellites. It will then be possible to locate any place in the region of South Asia and the Indian Ocean precisely.
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