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Why is LOGic's map distorted?
#1 Posted : Thursday, June 16, 2011 5:50:08 AM(UTC)

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All maps are distorted. This is necessary to represent the curved surface of a spherical object on a flat screen or piece of paper.

There are many map projections, each with its own compromises. For example, the Mercator projection, which is popular for typical wall maps, distorts several aspects of the earth. Directions are especially incorrect. That's why new hams in the US are surprised to learn that Europe is not East, but Northeast! Mercator projections also distort land area and distance, especially near the poles.

LOGic uses an Azimuthal Equidistant (Az-Eq) projection. This is the projection valued by hams for years because distances and directions from your QTH are always correct. The ARRL sells thousands of its ARRL World Maps, which uses the Azimuthal Equidistant projection.

The main disadvantage of this projection has been that a map must be custom-designed for each QTH. The ARRL World Map is a beautiful map with many features and operating aids, and is a real work of art (get yours here). But is precise only if you live in the center of the United States. It is close for the rest of the continental US, but gets increasingly useless as you get further from the center of the US. If you look in old issues of QST, you will see ads offering Azimuthal Equidistant maps drawn on your QTH. Now that computers are commonplace, everyone can have their own custom map!

Obviously an AZ-Eq is distorted, because it looks very little like what you see on a globe, especially to someone who has never seen an Az-Eq map before. Exactly how is the Az-Eq map distorted? The more distant a land mass is, the larger it appears. On a map centered on the US, note how Australia appears to have approximately as much land area as North and South America combined!

And here is another anomoly. Suppose that there is a nice little one-acre tropical island paradise that is exactly on the opposite side of the earth from you. What direction is the island? All directions, of course! How does this appear on the map? As a land area that runs all around the perimiter of the map, encircling everything else on earth! Try setting the Lat to 28 and Lon to -33 (be sure to zoom to Whole Earth). Where do you think this is opposite to? Click Show for a hint.
Click Show after calculating (or guessing BigGrin) to check your answer.

Here is how to calculate the lat/lon on the opposite of the earth from you:

  • Latitude: Merely reverse the sign of your latitude.

  • Longitude: If your longitude is negative, add 180. If your latitude is positive, subtract 180.

Try plotting this and see what the view is from the opposite side of the earth from your QTH!
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