The earth’s grid system
When lines of latitude and longitude are drawn on a map they from a grid with the parallels and meridians meeting at right angles are called graticules .the gird lines are numbered east and north of a point of origin. These lines cross to from squares and any place can be accurately located on a map by using this gird. The latitude and longitude are angles, measured in degrees “minutes of arc “and seconds of arc” with the reference to the earth’s centre point and surface point. A degree contains 60 minutes of arc and one minute contains 60 seconds of arc. The distance between two longitude lines is highest at the equator and decreases towards the poles. For example, the distance between each 100 longitude at the equator is about 1,113km. Whereas the distance between each 100 longitudes at 800 latitude is only about 193 km. similarly, area of a grid of 100 longitudes and 100 latitude from equator is about 1,224,902 sq km. the area decreases towards the poles because of decreasing grid size.
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