FLAT MAP FROM SPHERICAL EARTH.

We know the importance of google map today. How to make a map? Earth is spherical, how to flatten it? When we look at a piece of land, it looks flat. Because the area is small. Hence making a map of a small town is easy. When we stand at the sea-shore and look at the ocean, we see horizon where the sky seems to meet the ocean. Horizon appears because of earth's curvature.
A map is should be fairly accurate. It should help long distance traveller (ship, airplanes). It should also meet eduction needs. We are going to use projection method for making a map.
Imagine a 'earth globe' made out of glass. And a transparent real map is drawn on it. We also put a powerful LED lamp at the centre of the glass globe. Put a cylindrical lampshade made out of white p[aper around it. The lampshade should be just touching the sides of the globe. Now switch on the LED lamp. A map is projected on the cylinder. But north and south pole cannot be projected. Since the cylinder is open at both the ends. Now cut the cylinder and unroll it. You get a fairly accurate flat map which is real good enough for all practical purposes. This techniques is called Mecator's projection. It is still used and popular one. If we want the map of north and south pole one can use conical shades.

There are many projection methods. Nothing is perfect. There is some distortion in Mercator's method also. The regions near the pole's appear larger and the regions near the equator appears smaller. There is always some error when spherical surface is flattened. (can you flaten the skin of an orange fruit).
Even measuring distance on a spherical surface pose some difficulty. The units of distance measurement like kilometer, mile, yards -all fail on curved surface. Hence we use'nautical mile'.

Globe or sphere is a rotated circle. A circle has angle of 360 degrees. A degree is split into 60 minutes. One minute angle suspend an arc or distance on the surface of the earth. The length of the arc is 1852 meters. That is one nautical mile.
Our world is mostly curved one.
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