How to Measure Distances on a Globe
A globe offers an accurate means of measuring distances between any two points on Earth. Since the world is roughly spherical, the shortest distance between two points will be an arc, not a straight line. A "great circle" is any arc that represents the shortest distance between two points on a sphere, which means it is a line you can imagine if you cut the sphere into two equal halves. For example, lines of longitude (sometimes called meridians) represent great circles, as does the Equator. To measure distances on a globe, you must first find the great circle.
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Instructions
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Choose two locations between which you wish to find the distance.
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Lay a piece of string over your globe so that it touches both locations. Pull it taut. The string now represents a section of a great circle. If you cut the globe exactly along this line, the globe would be split into two equal halves.
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Mark the string where it touches each location. Use a pen or marker. Alternatively, hold the string so that the tips of your fingers mark the locations on the string.
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Lay the marked string along the equator on the globe.
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Add up the number of degrees that the marked string spans. The easiest way to do this is to place one marked end of the string at 0 degrees and then read the number closest to the other marked end.
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Multiply the number of degrees by 69.17, which is the number of miles per degree at the equator. The number you end up with is the distance in miles between the two locations.
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Tips & Warnings
Technically, the Earth is an oblate spheroid, not a sphere, since it is squashed at the poles. But the difference is slight enough that general measurements can treat the Earth as if it were spherical.
All flat maps distort the shape and size of the world in one way or another, but they allow people to visualize the whole world at once.
