Now let’s look at some voyages a ship might make. The trouble is, this makes countries near the poles so much larger in all directions that Greenland looks bigger than the USA, when in fact it has only about the same area as Mexico. To keep their shapes right on Mercator’s projection, these countries are also stretched in the north-south direction by moving the parallels of latitude farther apart as they get nearer the poles. This means that on Mercator’s projection, countries nearer the pole are stretched sideways, in an east-west direction. On the globe, of course, they get closer towards the poles. The meridians are drawn as lines that stay the same distance apart all the way up and down. A sheet of paper is wrapped like a cylinder round the globe, touching the equator all round. In atlases, maps of the whole world often use Mercator’s projection map. For places nearer the pole, a flatter cone is used, and for areas very close to the pole, a flat sheet touching the pole. When the cone is cut up one side and spread out flat the meridians will be straight lines and the parallels will be circles.Ĭountries close to where the cone touches the globe are roughly the right shape, and charts of fairly small areas can be used for navigation. To make charts of places in the latitudes of the USA or Europe, we imagine a cone of paper sitting over the north pole, and a light shining from inside the globe. If countries are fairly near the equator, we can put them at the center of the chart by turning the globe round, but for places farther north and south this won’t work. The different ways of doing it are called projections, because they start from the idea of shining a light through part of a see-through globe, so that the shadows of the parallels, meridians and the outlines of countries make a chart on a screen.Ĭountries and seas near the center of the chart will be roughly the right shape, so distances and directions can be measured accurately, but nearer the edges shapes will be all wrong and the chart will be useless for navigation. Now we can look at how the round earth is charted on flat paper. The 180° meridian is called the International Date Line because that is where each new day starts. On the other side of the globe, opposite the Greenwich meridian, and just west of Alaska, is the meridian that is both 180☎ and 180°W. Like latitude, longitude is measured in degrees. The distance east or west of any place on the globe, measured from the meridian through Greenwich in England, is called the longitude of that place. Lines drawn on the globe from the north to the south pole are called meridians of longitude. The latitude of New York is just over 41°N, which puts it in the “mid latitudes”. Places near the equator are in “low latitudes”, near the poles are “high latitudes”. The latitude of any place on the globe is its distance north or south of the equator, measured in degrees, from 0° at the equator to 90°N at the north pole and 90°S at the south pole. More circles are drawn, parallel to the equator, called parallels of latitude. On a globe of the world, a circle is drawn, midway between the north and south poles, called the equator. You need to know a few things before you can understand how this problem has been tackled, so here goes! The trouble is, nobody can make a perfect chart because the earth is a large ball and charts are drawn on paper, which is flat. Sailors need accurate charts to find their way around the seas.
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