The
scale of a
map is the
ratio of a distance on the map to the corresponding distance on the ground. This simple concept is complicated by the curvature of the
Earth's surface, which forces scale to vary across a map. Because of this variation, the concept of scale becomes meaningful in two distinct ways. The first way is the ratio of the size of the
generating globe to the size of the Earth. The generating globe is a conceptual model to which the Earth is shrunk and from which the map is
projected.