Local linear scale factors in map projections in the direction of coordinate axes

This paper explains that the terms "horizontal and vertical scales" are not appropriate in map projections theory. Instead, the authors suggest using the term "scales in the direction of coordinate axes." Since it is not possible to read a local linear scale factor in the direction of a coordinate axis immediately from the definition of a local linear scale factor, this paper considers the derivation of new formulae that enable local linear scale factors in the direction of coordinate x and y axes to be calculated. The formula for computing the local linear scale factor in any direction defined by dx and dy is also derived. Furthermore, the position and magnitude of the extreme values of the local linear scale factor are considered and new formulas derived.