1 [cartography] The reciprocal of the ratio used to specify scale on a map. For example, if the scale of a map is given as 1:50,000, the scale factor is 50,000.
2 [coordinate systems] In a coordinate system, a value (usually less than one) that converts a tangent projection to a secant projection, represented by “k0” or “k.” If a projected coordinate system doesn’t support a scale factor, the standard lines of the projection have a scale factor of 1.0. Other points on the map have scale factors greater or less than 1.0. If a projected coordinate system supports a scale factor, the defining parameters no longer have a scale factor of 1.0.