Map Projections. E-book. Formato PDF Arthur R. Hinks   -  Forgotten Books, 2017  - 

The scale of a map in a given direction at any point is the ratio which a short distance measured on the map bears to the corresponding distance upon the surface Of the Earth. We must limit our definition to Mort distances because the scale of a map will generally vary from point to point; hence in defining scale we must confine ourselves to small elements of distance in the way which is familiar to every beginner in the differential calculus.