Saturday, July 28, 2007

Why is the mercator projetcion used by Virtual Earth and Google Earth?

Ever wondered why they use the Mercator projection in Virtual Earth and Google Earth? Simple - its so that when we drive around and are looking at a map - North is up, South is directly below and East and West are directly opposite to each other and perpendicular to North South. (This is because the mercator projection is a cylinderical projection - the directions would be all messed up if it were a conical projection). In 2, observe that the meridians and parallels are equidistance, straight lines, with the two sets crossing at right angles, this is what makes north up and south down,...... Though the areas are all off. Which brings to the other important reason that this projection is used: Even though at global levels the areas are off, at local scales the shapes are preserved. So while vieweing objects in aerial imagery - the objects look like they should and not distorted (so square looks square and not rectangular or circles look like circles and not ovals).

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