How do you measure find the distance between two cities?

Answer 1

If the cities are close to each other, then you can treat them as if they were on a plane surface and the distance between them would be the scaled-up version of the distance between them on a map. However, if the cities are further apart then you need to take account of the fact that they are on a spherical surface. To do this you need to identify the plane which is defined by the two cities and the centre of the earth. This plane will meet the surface of the earth in what is known as the great arc, and the distance between the two cities is measure along the great arc. Incidentally, this is why flights from London to Tokyo, for example, fly over the North pole.