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`color{green}(โข)` To fix the position of a place, it is necessary to know something more than the latitude of that place.
`color{green}(โข)` You can see, for example, that Tonga Islands (in the Pacific Ocean) and Mauritius Islands (in the Indian Ocean) are situated on the same latitude (i.e., 20ยฐ S).
`color{green}(โข)` Now, in order to locate them precisely, we must find out how far east or west these places are from a given line of reference running from the North Pole to the South Pole.
`color{green}(โข)` These lines of references are called the meridians of longitude, and the distances between them are measured in โdegrees of longitude.โ
`color{green}(โข)` Each degree is further divided into minutes, and minutes into seconds.
`color{green}(โข)` They are semicircles and the distance between them decreases steadily pole wards until it becomes zero at the poles, where all the meridians meet.
`color{green}(โข)` Unlike parallels of latitude, all meridians are of equal length.
`color{green}(โข)` Thus, it was difficult to number the meridians.
`color{green}(โข)` Hence, all countries decided that the count should begin from the meridian which passed through Greenwich, where the British Royal Observatory is located.
`color{green}(โข)` This meridian is called the Prime Meridian. Its value is 0ยฐ longitude and from it we count 180ยฐ eastward as well as 180ยฐ westward. The Prime Meridian and 180ยฐ meridian divide the earth into two equal halves, the Eastern Hemisphere and the Western Hemisphere.
`color{green}(โข)` Therefore, the longitude of a place is followed by the letter E for the east and W for the west.
`color{green}(โข)` It is, however, interesting to note that 180ยฐ East and 180ยฐ West meridians are on the same line.
`color{green}(โข)` Now look at the grid of the parallels of latitude and meridians of longitude on the globe (Figure 2.6).
`color{green}(โข)` You can locate any point on the globe very easily if you know its latitude and longitude.
`color{green}(โข)` For example, Dhubri in Assam is situated at 26ยฐ N latitude and 90ยฐ E longitude.
`color{green}(โข)` Find out the point where these two lines cut each other.
`color{green}(โข)` That point will be the location of Dhubri.
`color{green}(โข)` To understand this clearly draw equidistant vertical and horizontal lines on a paper (Figure 2.7).
`color{green}(โข)` Label the vertical rows with numbers and horizontal rows with letters, draw some small circles randomly on points where these horizontal and vertical lines intersect each other.
`color{green}(โข)` Name these small circles as a, b, c, d and e.
`color{green}(โข)` Let vertical lines represent East Longitudes and horizontal lines as North Latitudes.
`color{green}(โข)` Now you will see that circle โaโ is located on Bยฐ N latitude and 1ยฐ E longitude.
`color{green}(โข)` Find out the location of other circles.
